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Composting Toilet Installation Considerations


Please note, complete installation information for each individual product can be found in the product instruction manual. Links to these manuals can be found on each product detail page.


Quick Links:
What's in the Box?
Installing the Vent Stack
Non-Electric Units: Do you need a 12 Volt fan? Which units already come with a fan?
Electrical Installation
Operation of One Pint Flush Toilets
Installation of One Pint Flush Toilets
Installation of Dry Toilets
Handling Excess Liquid - Drain Hookup


What's in the Box?

Composting Toilet Box Contents
Sun-Mar units are designed for easy do-it-yourself installation, and in most cases, everything you need to get your unit going will be included in the box. The only exception is for those purchasing a water flush Central system, in which case you will need to purchase the standard 3" plumbing pipe and fittings needed to connect the one pint flush toilet to the central composting unit. Here are some more details about what you'll find in the box with your composting toilet:

All units include:

Some other items:
  • 10' of 1" diameter drain hose and clamp is included with all units except the Excel and Compact
  • Roof flashing and diffuser for 2", 3", or 4" pipe, as appropriate, is included with all units except the Mobile
  • 6' of 2" pipe insulation is included with the Excel and Compact units only
  • Central systems include a removable evaporating tray for placing in the evaporating chamber below the drum screen
  • Central AF (waterless) systems include a 45" long pipe piece and waste inlet transition assembly to connect dry toilet to central composting unit
  • 3" waste inlet assembly (collar) piece is included with all water flush Central systems (however, you must supply the standard 3" plumbing pipe and other fittings needed to connect the one pint flush toilet to the central composting unit)

Vent Stack items:
  • A diffuser for the vent stack is included with all units except the Mobile. This simple but effective device is designed to aid updraft, avoid winter freeze up, and protect the vent from downdraft and weather.
  • All electric units come with 2" vent stacks of 10' and 15' respectively (central vacuum pipe). Also included are the necessary connectors, two 45 degree fittings, and one 90 degree elbow.
  • All non-electric units come with 4" vent stacks of 8' and 13' respectively (sewer pipe). Also included are the necessary connectors.
  • Non-electric Central AF (waterless) systems will also include two 45 degree elbows
  • All AC/DC (combination electric/non-electric) units have a complete 4" vent kit as described above, as well as the 2" vent kit.
  • The Excel AC/DC and Centrex 1000 AC/DC also include a 1.4 watt 12 Volt fan.
  • AC/DC units in the Centrex 2000 and 3000 families come with a 2.4 watt 12 Volt fan.
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Installing the Vent Stack
All composting toilets need to have the vent stack connected to the unit and erected as straight as possible to the roof with no horizontal runs. All electrical units use a 2" vent pipe, non-electric units use a 4" pipe, and Mobile units use 3" pipe. The vent kits included in the shipping carton are usually sufficient for installation in a single storey building. If more pipe is needed, you'll have to purchase it on your own from a hardware store or lumber mart.

Vent Installation Tips:
  • Electric units with 2" vents should have the minimum number of bends, which should not exceed 360 degrees total. 45 Degree elbows should be used wherever possible. No pipe run should be horizontal, no matter how short.
  • 3" And 4" vents should be installed as straight as possible. If a 4" vent requires 45 degree elbows, then a 12 Volt fan should be included in the vent stack.
  • Merging a composting toilet vent with other existing vents risks interference and is not advised.
  • The vent stack diffuser should be installed at least 2-3 feet above the roof (and higher, if at all possible), as shown in the diagram below:

Composting Toilet Venting    Composting Toilet Diffuser

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Non-Electric Units: Do you need a 12 Volt fan?
A 12 Volt fan is not normally needed with the Excel NE, Centrex 1000 NE, and Centrex 2000 NE. With a vertical 4" vent stack, the chimney effect ensures there will be no odor in the bathroom. The Composting Toilet Store does have 12 Volt fans available for purchase separately, should one ever be needed.

We do recommend installation of a 12 Volt fan in 4" vent stacks under the following circumstances:
  • If the unit is to be used residentially or heavily
  • If the vent stack has one or more 45 degree angles
  • IF the installation is subject to downdraft, being in a valley and/or surrounded by tall trees
Which units already come with fans?
UnitType of Fan Included
Excel AC/DC12V 1.4 Watt Fan
Centrex 1000 AC/DC12V 1.4 Watt Fan
Centrex 2000 AC/DC12V 2.4 Watt Fan
Centrex 2000 AF NE12V 2.4 Watt Fan
Centrex 2000 AF AC/DC12V 2.4 Watt Fan
Centrex 3000 NE12V 2.4 Watt Fan
Centrex 3000 AC/DC12V 2.4 Watt Fan
Centrex 3000 AF NE12V 2.4 Watt Fan
Centrex 3000 AF AC/DC12V 2.4 Watt Fan

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Electrical Installation:
All electric units are supplied with a power cord, which plugs into a standard three prong 110/115 Volt outlet. This plug powers both the fan and heating element in electric units.

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Operation of One Pint Flush Toilets:
The most popular type of central systems are water flush units which use the one pint flush toilets. The water flush and water seal of the one pint flush toilet ensures odorless operation, and makes these units most similar to a traditional toilet. A ceramic one pint flush toilet in the bathroom (available in white or bone colors) is connected to the Centrex central composting unit in the basement with standard 3" plumbing pipe, which you must provide yourself (it is not included with the units). The central composting unit should be placed below and within 15-20 feet of the one pint flush toilet.

One pint flush toilets have no water tank. They are flushed by a foot pedal which opens a water valve, discharging waste while pushed down, and filling the bowl when lifted. After flushing, a small amount of water is held in the toilet bowl, which is sealed by a teflon and rubber seal. Even gravity fed water from a roof tank is sufficient to flush the one pint flush toilets, and in winter, they can be flushed manually using a container.

More than one toilet can be installed with Centrex water flush systems. The limitation is the number of people using the unit rather than the number of toilets connected to the unit. The standard one pint flush toilet is Model 510+, which offers a regular sized bowl and toilet seat, with 17-1/8" height. In some instances, extra height is needed to allow the toilet to gravity feed to the composting unit. Where this is the case, the Model 511+ (low profile model) with a 13" seat height can be mounted on a platform, and the waste pipe can then go out above the floor, which reduces the installation height needed.

Composting Toilet Installation
Composting Toilet Installation

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Installation of One Pint Flush Toilets:
  • Mount toilets to the floor with a 3" diameter four bolt flange (sold separately), and connect your water supply to the 1/2" MPT fitting at the rear of the toilet. You will require a 1/2" FPT fitting to mate your water supply with this fitting on the toilet (not supplied, you will have to provide your own).
  • Connect the 3" DWV plumbing pipe (not supplied, you will have to provide your own) from the toilet to the composting unit. The waste pipe should be installed 45 degrees or more to the vertical, and/or a 2 to 3 degree angle (that is a drop of 1/8" to 1/4" per foot) so that the waste travels with the liquid.
  • Install multiple toilets using a "Y" fitting above the waste inlet of the composter.
  • Limit horizontal distances to 15-20 feet wherever possible. If the toilet is placed farther away, clean-out fittings and extra flush throughs will be needed, and difficulties may occur.
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Installation of Dry Toilets
  • Only one dry toilet can be installed per Centrex AF (waterless) system. Multiple dry toilets are not possible.
  • Bolt the dry toilet to the floor immediately above the waste inlet of the Central AF (waterless) composting unit. The toilet chute extends 4" below the toilet base so that it can sleeve into the 45" long waste pipe piece, or directly into the waste inlet transition piece. The 45" long 10" diameter pipe piece supplied can be cut to size, so the toilet mounting surface can be anywhere from 36-1/2" to 81-1/2" above the surface the Central composting unit is placed on.
  • The maximum recommended height of the waste inlet pipe assembly is the length of the pipe piece (45") plus the waste inlet transition piece (5"). Adding additional pipe lengths, while possible, may make it more difficult to ensure there is a downdraft at the toilet seat. This downdraft is what ensures odorless operation.
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Handling Excess Liquid - Drain Hookup:
Electric self-contained units (the Excel, Compact, and Spacesaver) and all electric Central AF (waterless) systems will evaporate all liquids under normal operation. Even so, as a safety precaution, we recommend that the safety drain be connected in every installation. Here are some tips for hooking up the drain:
  • Collect and/or treat excess liquid in an approved facility such as a recycling bed, old septic system, holding tank, or drain pit.
  • To make a closed loop system that does not touch the environment in any way, simply dig a recycling bed 18" deep and line it with a plastic sheet. Depending on the model of composting toilet, this bed will typically be from 3 to 25 feet square. Fill the bed with 6" of gravel, 12" of sand, and plant with grass or shrubs. For more information on recycling bed construction, please see Sun-Mar's simple Recycling Bed Construction Guide, or contact Sun-Mar directly at 888-341-0782.
  • Before installing any recycling bed or french drain, be sure to first check with your local building officials. It's important that your safety drain installation conforms to your local building code regulations.
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