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
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
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
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:
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
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
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
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)
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
Toilet cabinet with lid up.
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.
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.
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.
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
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
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
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).
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
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
page. The bucket is then rinsed and returned to the toilet area.
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.
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
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
2) Bucket is dumped into
barrel, then bucket side is slapped several times to dislodge any
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
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
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
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
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
-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
-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.
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