Bucket-to-Barrel Composting Toilet System

(Page updated 12/27/2011)

For additional information, see our other composting toilet web pages:

-Barrel Composting Toilet

 

Note: The Bucket-to-Barrel Composting Toilet system described here involves using a 5 gallon bucket as a toilet receptacle.  When the bucket is full it is emptied into a 55 gallon barrel.  Regulators tend to look unfavorably on bucket systems due to the increased chance of contamination when emptying buckets.  To address this, we have developed a variation called the Barrel Composting Toilet system.  In the Barrel Composting Toilet system, the barrel is fitted with a toilet seat and vent and is used directly. With this modification, a permit might be granted for the system in some jurisdictions.  In terms of capacity and pathogen treatment levels, the two designs are identical.  For more information see our Barrel Composting Toilet webpage.        

Bucket-to-Barrel Composting Toilet system description:

Since 2005, we have been developing and using a composting toilet design that is simple, inexpensive and easy to replicate, yet also meets most of the design considerations addressed on our Composting Toilet Regulations page. The system is constructed of 5 gallon buckets and 55 gallon plastic barrels. Most of the materials can be purchased at a hardware store and the cost of the system is about $250, (assuming a 3 barrel system and new materials).

The system features vector control, zero leachate discharge to native soil, aeration, moisture control of the compost and construction of durable, non-corrosive materials. Although the system is designed for use in mild climates, we've used it in places as diverse as Arizona and Oregon. The reason for use in mild climates is that the composting chambers are outdoors and sufficient warm weather is needed during the year for proper composting to take place. For more information, see our Guide to Appropriate Climates for Outdoor Installations webpage.  In colder climates, the barrels must be located inside a building, preferably heated, where it is protected from temperature extremes. 

This system requires occasionally emptying buckets containing fecal matter and is therefore not for the fecophobic. However, it is not the smelly, objectionable process that one might imagine it to be. The buckets contain mostly odorless cover material and the process requires only about 15 minutes every couple weeks.   Since the 5-gallon toilet receptacle is small, it can easily be fit into an existing bathroom.  

I believe this system performs as well as any certified composting toilet in terms of pathogen destruction and nitrogen levels despite its simple design. Unfortunately, it is doubtful, given the current regulatory climate, that it could be permitted. Regulators are typically cautious about what they will grant permits for and most feel that a toilet system requiring manual emptying of buckets containing feces into a composting chamber involves too much risk of contamination. Obviously, preventing communicable disease should be taken seriously. On the other hand, it's not nuclear waste that is being handled. Indeed, it is difficult to see how the risk of contamination during routine maintenance of a bucket toilet system differs significantly from cleaning oneself after defecation. In either case a similar risk of contamination exists requiring similar precautions (especially hand washing). I know of many people (including a medical doctor) who have been using bucket toilet systems for many years without problems. Hopefully, the perspectives of regulators will change as bucket toilet users accrue more evidence of the relative safety of such systems.

In the bucket version of the system, which is what we use, separate 5 gallon buckets are used for defecation and urination. Buckets containing feces and cover material are periodically emptied into composting chambers made from 55 gallon plastic barrels. Urine, which is collected in a separate bucket, is diluted with water and emptied daily into mulch basins around trees and shrubs. The number of buckets and barrels used is flexible and is based on the number of people using the system.

Composting toilets address only one aspect of the wastewater flow.  For a description of our current blackwater and graywater systems, see our Water Reuse page.  

Following is a description of the composting toilet system components and processes:

 

Toilet Bucket:

The toilet receptacle consists of plastic 5 gallon buckets.  For 2 adults in full-time use, three buckets are a convenient number, allowing about 2 weeks of use before buckets need to be emptied.  Each bucket should have a gasketed, leak-proof lid and can be purchased from hardware stores for about $6, including lid. The toilet buckets are used primarily for defecation, although the system accommodates urination that occurs during defecation. As the photos below show, the toilet buckets can be located either indoors or outdoors. 

 

Outdoor version:

Our outdoor toilet in Arizona is located behind a privacy screen of mesquite branches. The toilet was constructed by cutting a 5 gallon bucket in half to make a base and a top for the toilet bucket. The bottom 8 inches of the cut bucket serves as a base to stabilize the toilet bucket while in use. The base is buried in the ground about 6" deep. A couple inches of sand are put into the bottom of the base to help prevent the toilet bucket from becoming stuck in the base. A plastic toilet seat/lid, available from camping supply stores for about $5, is snapped onto the top portion of the cut bucket. This makes a seat assembly which is inserted into the toilet bucket. The function of the seat assembly is to keep the bottom of the toilet user several inches higher above the toilet bucket contents, which allows the toilet bucket to be filled somewhat fuller before it needs to be replaced.

This outdoor toilet has no roof. If it rains, we use an umbrella.  It's really quite pleasant.

Outdoor toilet in remote site (Arizona). From left to right--gray bucket contains toilet paper. Toilet bucket with snap on lid/seat. 1 qt. water bottles for moistening toilet paper. Container of cover material. Two extra toilet buckets. (Urine bucket not shown.)

         Toilet bucket details. Seat assembly (being held above        toilet bucket) slides down into toilet bucket. Toilet bucket goes in  base (at left) and is ready for use. (see description above)

 

Indoor version:

Our indoor toilet in Oregon consists of a 5 gallon bucket inside a wooden cabinet with hinged lid.  The cabinet is made from 3/4 inch plywood.  The cabinet has no bottom.

Indoor toilet. Note bucket of cover material containing wood shavings on right and urine bucket on left.

Toilet cabinet with lid up. 

Composting Barrel:

The composting chambers are constructed from food grade, polyethylene barrels purchased in nearly new condition (used one time only). They can be purchased from bakeries and feed stores for about $15 apiece, or check the yellow pages under "barrels".

If used barrels are utilized, they must be checked for UV damage, which can make them brittle.  Lay a barrel on it's side and press your knee on it, forcing it to indent several inches.  Listen for any cracking sound.  Now rotate the barrel and try it again.  Do this around the entire circumference of the barrel.  If you hear or see any cracking, the barrel is unsuitable.   

The top of the barrel is cut out about 2 inches in from the edge using a power sabre saw.  If you cut them close to the edge, the barrels will tend to become somewhat oblong at the top rather than round.  This does not affect the proper functioning of the barrels however.

The barrel is then painted a dark color using oil based paint.  This protects the barrel from UV deterioration and helps with heat absorption from sunlight. If located outdoors, the barrels should be in a sunny location. In windy locations, the barrels must be secured to prevent tipping over.  One simple way is to bury them about 1 foot deep in the ground, although this makes a somewhat less convenient height for emptying buckets and aerating. 

Vector Control:

For insect vector control, a 3 foot diameter piece of fiberglass screen or insect netting is secured around barrel tops using a piece of 1/8 inch nylon cord about 8 feet long and a spring. The cord is adjusted so that the spring provides a light tension, yet allows the cord to be removed and replaced quickly and easily. For animal vector control and to prevent rainwater from entering the barrels, each barrel is covered with a lid of galvanized corrugated roofing 27 inches square. The corrugations permit airflow to the compost.  The lids are secured with masonry blocks. 

Also see "Insect Trap" section below.

Sizing the System:

Barrels are filled to within about 6-8 inches of the top. One barrel is filled at a time.  To help insure pathogen destruction, a sufficient number of barrels are used to allow feces to compost for a minimum of 4 months.  In full time use 2 adults will fill one 55 gallon chamber in about 2 months, requiring 3 barrels for a 4 month retention time.  For 3 adults 4 barrels are required, for 4 adults 5 barrels are required, etc.       

1) Compost chambers made from 55 gallon polyethylene barrels.

 

2) Lid made from corrugated metal roofing secured with masonry blocks.

 

3) Lid with blocks removed.

 

4) Insect screen with lid removed.  Note cord and spring for securing screen.

 

5) Detail of cord and spring for securing screen. Spring is 5/16 inches in diameter by about 5 inches long. Cord is 1/8 inch nylon about 7 feet long.  Cord is knotted into ends of spring.

6) Top of chamber with screen removed. Object in center is compost thermometer.

Cover material:  

In Arizona, we use mesquite duff (dry and partially decomposed leaves) which are raked up from under large mesquite trees.  This is passed through a 1/2 inch hardware cloth to separate out twigs and other debris. We take care to rake up as little dirt as possible with the duff.  In Oregon, we have been using purchased wood planer shavings for cover material (these contain no treated wood shavings). The wood shavings are clean and pleasant to use, but take a long time to decompose, so we're considering switching to shredded leaves.

Also see our Cover Materials webpage.

Mesquite duff (leaf) cover material used in Arizona.

 

Wood shaving cover material used in Oregon.

 

Using the Bucket-to-Barrel Toilet:

A variety of bucket arrangements are possible, but essentially they all work the same.  When a toilet bucket is about 3/4 full, a lid is snapped on, the bucket is removed and a clean bucket is put in it's place.  A few cups of cover material are added to cover the bottom of the bucket and it's ready for use.  A bucket containing cover material is located conveniently beside the toilet (more on this below). 

After each use, enough cover material is added to completely cover all feces and toilet paper (typically 3 to 6 cups per use). We keep a 1 qt. plastic bottle with squirt cap next to the toilet for moistening toilet paper after use. This serves several purposes.  It reduces the volume of the toilet paper, it allows the toilet paper to be covered using less cover material and it greatly reduces the decomposition time.

With 2 adults using the system full-time, it takes about 2 weeks to fill all 3 toilet buckets.  The buckets are then emptied into an outdoor composting chamber constructed from a 55 gallon barrel. The compost in the barrel is manually aerated each time buckets are emptied (i.e. at least once every 2 weeks).  

Urine management:

This system is designed as a zero discharge system, meaning that all liquid (leachate) remains in the barrel, where it eventually evaporates. There are no holes drilled in the bottom of the barrels. The leachate includes the small amount of urine excreted during defecation as well as the small amount of water used in bucket cleaning.  Because of this, a urine management system is an integral part of the design. 

A separate 5 gallon bucket with lid is used for urination only. The urine bucket is emptied on a daily basis, either full strength onto a compost pile to provide extra nitrogen, or diluted with at least 3 parts water to 1 part urine and emptied into mulch basins around shrubs or trees as described on our Water Reuse page. The bucket is then rinsed and returned to the toilet area.

Aerating compost:

The aeration process is done each time buckets are emptied, or at least every 2 weeks, and is done before emptying buckets.   The barrel with the oldest material is aerated first, then the barrel with the next oldest material and finally the barrel that is about to be emptied into.  This helps prevent contamination via the Compost Crank from fresher material to older material.   

Since the composting barrels have no air vents or leachate drain, thorough aeration, moisture control and mixing of the compost are particularly important. In the process of developing this system, we tried a variety of manual compost aerators without success. Finally we discovered the Compost Crank. This well designed tool is made of stainless steel and works far better than any other aerator we've tried. The Compost Crank pulls wet material up from the bottom of the composting chamber, effectively aerating the compost and distributing moisture throughout the compost.  The cost of the Compost Crank in late 2011 is about $45. (Note: We have no financial connection with the manufacturer of this tool).

The tool is cranked into the compost until the spiral end contacts the bottom of the barrel. Without further cranking, the tool is then pulled straight up until the spiral end reaches the surface of the compost. The process is then repeated in another part of the compost until all compost is thoroughly mixed and aerated (a dozen times or so is about right). If the compost is heavy or clumpy, it will be easier to aerate only a foot or so deep, then repeat, going deeper each time until the Compost Crank reaches the bottom of the barrel.  Thoroughly aerating 3 barrels takes about 10 minutes. 

The Compost Crank is stored in a 30" length of 4" diameter plastic pipe when not in use. The pipe can be buried in the ground.  If small children are present, the bottom of the pipe should be fitted with a cap and the pipe secured so that it is high enough to be out of reach.  

 

 

1) Compost Crank

 

2) To use, crank tool until spiral end reaches bottom of barrel.

 

3) Without turning crank further, firmly grab handle.

4) Slowly pull crank straight up until spiral end of Compost Crank reaches surface of compost. Repeat in another part of compost until all compost is mixed and aerated. Replace screen and lid on barrel. Not shown is the final step, which is hand washing.

A holder for compost crank made from 4" ABS pipe about 2' long.  Pipe is buried in the ground about 1'.

Finished compost.

 

Emptying buckets: Toilet buckets are emptied when all 3 buckets are full. 1 qt. plastic bottles with squirt caps are filled with water and used to rinse buckets. One bottle is used for cleaning each bucket although only 1/3 or less of each bottle is used. To prevent contamination from spray, pressurized water from hose or other source should not be used. Emptying and cleaning 3 buckets takes about 10 minutes. Hand washing is the final and most important step in the process.

1) Full buckets are carried to compost barrels. Note stand with spray bottles and toilet brush at left.

 

 

2) Bucket is dumped into barrel, then bucket side is slapped several times to dislodge any remaining material.

 

 

3) After dumping, bucket is rinsed with water.

 

4) Bucket is scrubbed with toilet brush, then water is dumped into chamber.

 

5) Bucket is rinsed again and rinse water is dumped into chamber. After all buckets are emptied and cleaned, screen and lid are replaced on barrel.

 

 

6) Bucket is turned upside down to drip, then a few cups of cover material is put into bottom of bucket and bucket is returned to toilet area.  Hand washing is the final step in the process.

 

Emptying compost chambers: After 4 months of composting (since the last bucket was emptied into it) the composted contents of a barrel are emptied into a wheelbarrow using a shovel. It is common to assume that this is a difficult task.  It isn't.  Typically it takes us about 15 minutes, including screening. 

Lay an old sheet or tarp on the ground and set a wheelbarrow on it.  Place a screen of 1/2" hardware cloth on top of the wheelbarrow.  Shovel compost from the barrel onto the screen.  Any compost that will not pass through the screen is dumped onto the sheet (typically, there will be a few gallons of material that don't pass through the screen).  When the barrel is nearly empty, it can be turned upside down to empty the last bit of the compost.  The sheet is then gathered up and the larger pieces of compost are dumped back into the barrel for another 4 months of composting.  The barrel is then ready to be filled again and the cycle is repeated.

The screened compost compost makes excellent mulch/fertilizer around trees and shrubs.  We also use it as the the growing medium in our salad garden, but in that application, we further age it for a minimum of 1 year before using. 

Empting a compost barrel

 

Insect Trap:

Making and installing an insect trap in each barrel is recommended and is described in detail below.  (More information on insect traps can be seen on our other composting toilet pages.)

3-1/2" diameter hole carefully cut in side of barrel (top of hole is about 2" below top of barrel)

 

Finished hole (a half-round file is used to smooth edge of hole)

 

                 Trap receptacle is made from 2 pieces of a 3" ABS pipe coupling and a 1-3/4" long piece of 3" ABS pipe

 

            Cutting the 2 pieces of 3" ABS pipe

 

One piece of coupling is slipped over the pipe and glued.  The coupling/pipe assembly is then inserted into hole in barrel and second piece of coupling is glued to pipe on inside of barrel. 

 

   Coupling/pipe assembly installed in barrel.  Strap is bolted to barrel and will secure trap in barrel.  Note adjustable buckle on strap.

Trap components include canning jar, top of 1/2 liter plastic drinking water bottle and canning ring.

Marking plastic bottle for cutting. 

Cutting bottle with sharp knife. 

Parts for trap ready to assemble.  Top of plastic bottle is inserted into mouth of jar and secured in jar with canning ring. 

Assembled trap.  Note that top of plastic bottle has been marked and cut cut at an angle.  It is then inserted into the canning jar so bottle mouth angles upward inside jar.  Insects are attracted upward toward light, so upward angled bottle allows them to enter the jar more easily.

Finished trap installed in barrel.

 

 

                        Barrel composting chambers showing installed insect traps.  Traps will be most effective if they face south, as more sunlight will enter them, attracting more insects. At right are the compost crank and screen for sifting finished compost.  Note stand for bottles and toilet brush used to clean buckets. 

 

Statistics: Here are some technical details:

-cover material use is 3 to 6 cups of cover material per person per day (although this is more than necessary for composting, we prefer to thoroughly cover all deposits for aesthetic reasons)

-for 2 people in full-time use, a 5 gallon bucket will be filled 3/4 full in about 3-4 days

-for 2 people in full-time use, one 55 gallon barrel will be filled in about 2 months

-for 2 people in full-time use, about 0.5 to 1 gallon of urine per day will accumulate in the urine bucket

-as average ambient temperatures vary from summer to winter in Zone 8 or higher climates, compost temperatures will vary from  60 to 80 degrees F in winter to 80 to 115 degrees F in summer.

 

2011 Update:

We have been using the Bucket-to-Barrel Composting Toilet system for 5 years.  It has met its design goals of simplicity, low cost and ease of replication.  We find the system safe, easy to use and odorless.  The visual appearance of the compost indicate excellent decomposition.  

As noted above, most regulators are uncomfortable with the bucket emptying aspect of such a design, as they feel it involves too much handling of fresh fecal matter.  In an effort to move toward a design that would be easier to permit in some jurisdictions, we are transitioning toward a functionally similar design we call the Barrel Composting Toilet System. 

 

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