A Low Cost Site-Built Composting Toilet System

Copyright © 2006-2009
R.L. Crosby, Biorealis Systems, Inc


There is tremendous worldwide demand for safe, reliable, affordable sanitation systems able to provide the convenience of flush toilets in locations where water supplies and wastewater disposal options are limited. Aerobic composting toilets offer one viable solution to the problem. Existing commercially available units generally fall into two categories: units sized for small families and/or weekend cabin use, costing about $1,500-$2,500 (e.g.BioLet, Envirolet, Sun-Mar, etc.); and larger, full capacity units sized for larger families and full-time residential use (e.g. Clivus Multrum, Phoenix, AlasCan, etc.). These units typically start at about $6-7,000, and go up from there, with installed costs reportedly running as high as $25,000.

Neither option provides a satisfactory solution to the general problem. The smaller units tend to be inadequate for full time residential use and require more attention and energy (manufacturer's claims notwithstanding), while the larger units are generally priced beyond the reach of those who need them the most.

Following is a description of a simple, large capacity composting toilet system developed by Biorealis Systems, which can be owner-built for less than the cost of typical smaller units, yet provide performance and features not found on systems costing far more. The complete system, including rotating turntable with three removable composter modules, plywood enclosure and urine-separating waste chute, can be built for less than $500 in materials and a couple of weekends' worth of labor. (Costs may be even lower, depending on availability & local cost of used drums, etc.)


  • Batch feed: There is no contact between finished compost and fresh waste. All material removed from the unit is fully aged and can be handled safely.

  • Modular: Modules can be added or removed as desired to accommodate any requirement, from single family, to multi-family, to institutional.

  • Low maintenance: No moving parts to fail. Only non-corroding materials in contact with wastes. Periodic maintenance requires removing, emptying and replacing a plastic drum - which can be done off site. Removed material is completely aged, light, odor-free humus. Modules can easily be handled by one person, and will fit through a 30" doorway.

  • Low energy use: Aeration/evaporation system uses exhaust air from existing household ventilation system (If none exists, one can/should be added, which would also address other health issues - i.e. indoor air quality). No other energy input is required.

  • Simple Design: Can be locally built, using commonly available materials. Does not require specialized tools or skills to build, lends itself to local self-help solutions, creation of local jobs, small business opportunities.


All designs involve compromise. This design is based on over 20 years of trial and error, design and redesign. During that time we have explored a wide variety of options and gained some definite ideas about what works and doesn't work for us. If you absolutely cannot live without a water flush toilet, and/or can't locate a waste chute directly above the composter, this isn't for you. Be advised, however, that if you can find a way to separate urine from the feces, and eliminate the extra water required to flush a toilet, you will greatly simplify both installation and maintenance requirements.

Construction detail photos:

Carousel Construction:

An easy way to draw a large circle on a sheet of plywood if you don't have a template or giant compass.

Cutting out the circle with a jigsaw.

The rotating platform, painted, with holes cut & drilled per drawings.

Heavy duty caster (three required).

Completed turntable, with casters and ball-bearing turntable installed.

(Note: In updated version described in construction manual, the turntable and base shown at center have been deleted -- as not necessary.)

Module Construction -- Preparing the drum

Preparing used 55 gal plastic drum, cutting out the head with a jigsaw. Other options include using open head drums, or steel drums with plastic liners, depending on what is available.

Drill hole in bottom of drum for mounting companion flanges. Hole saw used for center hole, spade bit used for bolt holes.

Hole pattern, flange, gasket & bolts.

(Note: In updated version described in construction manual, companion flanges are replaced with a bulkhead fitting. It is simpler and less expensive than flanges.)

Pair of flanges mounted to bottom of drum create bulkhead fitting for module drain. Pipe inserted in inner flange extends up inside perforated inner baffle assembly to provide standpipe & sump. Module drains to flat tray below turntable.

All three drums, upside down.

Module Construction -- Internal Baffle Assembly

Marking and cutting horizontal baffle plate.

Drilling holes in baffle plate. Perforations provide aeration and drainage from composting mass above. Cover with plastic screen.

Note: A less labor intensive option would be to use perforated plastic sheet. (At time of this writing, perforated sheet was somewhat more expensive than solid.)

Baffle plate with holes drilled and pipe caps glued to it.

Finished baffle plate with pipe legs attached.

Completed baffle assembly showing plate and perforated air tube. Air tube will be capped with a deflector cone, and wrapped with fiberglass insect screen, not shown.

Base of air tube (shown setting on flange, to show the alignment of holes & bolts.

Complete baffle assembly shown inside drum. Deflector cone at top of air tube and screens not shown.

Completed composter: three modues mounted on rotating turntable platform.

Waste Chute Construction

Making a waste chute from a sheet of plastic. Shown with edge place in clamp, getting ready to glue. (Construction Manual includes information on how to make the clamp.)


Plastic sheet rolled into cylinder, still in clamp waiting for glue to harden. Funnel shown in background is modified and mounted inside front edge of chute for capturing and separating urine from feces. (Note: total cost for materials for this toilet is approximately $35. Compare to commercially available units such as the Swedish Separett, (available in the USA from Ecovita), costing closer to $1,000 each. More information about the benefits of urine separation is available in Construction Manual sample pages linked below.)

Copyright © 2002-2009 Robert .L. Crosby Jr; Information on this page may be copied, distributed and/or modified under certain conditions, but it comes WITHOUT ANY WARRANTY; see the Design Science License for more details.


Construction Manual

Includes detailed step-by-step assembly instructions, fully dimensioned drawings and specifications, materials list, tools required, links to additional resources and larger format photos.

36 - 8-1/2" x 11" color pages, plus 4 Sheets of 11" x 17" drawings: Sample Pages (328K PDF)

Purchase Options


(Shipping costs apply to printed hardcopy only)

construction drawings