GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Toilet and greywater system for external apartment

robbrown99 | Posted in Green Products and Materials on

We have a 900sq ft apartment in MA above our detatched garage that is plumbed in, has electricity but no sewage or greywater treatment. A couple of owners previous to us 25 years ago had installed a tight tank and the apartment was fully functional (kitchen, bathroom with sink, shower/bath and toilet). However they did this without the town knowing and when they sold the town had them crush the tight tank system.

We are on an old septic in the main house (limited to 3 bed, installed 1969) and are thinking about how we can get the apartment plumbed in so that:

1. The toilet works (there is an existing toilet).
2. The sink for kitchen (no need for dishwasher) and greywater water from bathroom can be dealt with.

The apartment is on MA recognized wetland, so we will likely have to get special permission to do any work when connecting outlets outside the building.

1. Build an entirely new septic system away from the apartment that can handle the apartment and the house. I would expect that to run into the tens of thousands (maybe $50K+), but perhaps the ’69 unit will not last much longer.

2. Install some form of foaming / composting / incinerating toilet such as Clevus. Have a holding tank in the garage for the solids / whatever processing unit is necessary (there is room at the back). Also install a greywater treatment system that outputs clean water that we can simply drain away. Does greywater actually have to be treated in MA?

Has anyone done a similar kind of job?


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Rob Brown,
    You need to do some research. First, you need to talk to an engineer who designs septic systems -- someone who is familiar with the regulations in your jurisdiction. The engineer should be able to visit your site and give you some preliminary feedback about your options.

    Not all municipalities allow the installation of composting toilets. Note that composting toilets take up a big volume of space on the floor directly under the toilet. Call up your local building department to get some information.

    Remember, plumbing pipes and drain pipes in this type of bonus room can freeze. Talk to a plumber about freeze protection for all of the plumbing you anticipate installing.

  2. robbrown99 | | #2

    Thanks Martin, will reach out to a local septic company that advertises alternative solutions also.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |