Help! Designing Code-Compliant Greywater System

We are building a workshop and living space that will be designed under our ten-mile building challenge rubric, that is, everything must come from less than ten miles from the build site, on average. Part of this is dealing with our waste stream as the building is in use. To that end, we’re designing a plumbing system that consists of a listed composting toilet for “blackwater” and then a “greywater” system to exfiltrate the sink and shower drain water. The composting toilet has been easy to manage because they come ready to install. But in the state of Wisconsin, a greywater system requires the services of a registered designer of plumbing systems. It must be approved at the state level.

The System Design

We have already spoken with an out of state greywater design firm, who sketched out the system that would meet code, but as they are not licensed here, we cannot use their services. Essentially, it is a steeply sloped drain pipe (1 in over 4 ft) buried in a trench of woodchips which are exchanged every three years. In our loamy and sandy clay, we’d need 75 ft of drainage to deal with the 60 gal/day of greywater stipulated by the state for a single bedroom, single bath habitation.

We have an adjacent four-season greenhouse where the drain field could be installed to help irrigate above-ground plants safely (and with less need to excavate below the frostline).

We cannot use a septic or holding tank in this space due to access issues.

The Problem

We’ve got the specs, we’ve got the design, we have a master plumber interested in the install, and we’ve emailed all the designers of plumbing systems in the state’s list (and followed up by phone). The few who responded said they only do commercial systems, but the design would be easy.

The big problem is that this isn’t done to code much in Wisconsin, so no one has an “off the shelf” model to modify for a quick and easy design here. Basically, it would take more work than it is worth, or so I’ve been told. But I know a niche market for this type of design is out there, because I hear from people asking for information about doing this up to code.

Without sorting out this design to the state’s requirements, we cannot build a habitable space into our workshop, the entire reason for the build! We want to show that it is possible to make a warm, comfy, attractive house in a locally sustainable way.

If you, or someone you know can help us with this design, please either forward this to him/her or send any leads to

2 thoughts on “Help! Designing Code-Compliant Greywater System

  1. I talked to a plumber I know and he said your Master Plumber should be able to figure it out. Either by calling him/herself the designer or by chasing up their supply chain and vendors to verify things are ok with the state. Not sure if that’s perfectly true, he’s a bit of a good ol boy out here in the country (in WI)

Leave a Reply