The Watson Wick Alternative Septic System

This is another article written by Kyle for Mother Earth News Magazine.

Humanure composting is an adventure.  There’s the buckets of waste and sawdust to take out every few days, no excuses. There’s the three or more compost bins to build and finding sources of sawdust. There’s ventilation in the bathroom and maybe adding ash to mitigate smells. And urine: to collect separately or to let it all mix together? How long to compost? Two years? More? What about guests? How will they feel about having just a bucket under their tuckus?

The upshot is that, in order to make humanure composting a success, it takes equal parts work, gumption, and creativity. But it also yields amazingly good compost for perennials, keeps nutrients close — real close — and transforms what would otherwise be a gross, intensively-treated waste product into a valuable resource for your soils and garden.

At my friend Gus’ place, he’s done this successfully for seven years. But as they started welcoming kids to their space through camps and programs, they realized they needed a standard flush toilet to ensure everyone was comfortable and there weren’t any issues with kids and parents and a bucket in a box. Their solution was the alternative and technologically appropriate Watson Wick Septic System.

I learned of this system from a friend in New Mexico who learned about it from Tom Watson himself, maybe 20 years ago. She wound up installing a Watson Wick System in her urban home about 15 years ago, and it’s been functioning perfectly ever since. The design is simple, the setup is easy and low-cost, the function is hassle- and worry-free, and the results are marvelous.

After hearing about it, I started researching online and found very little out there; this article from Oasis Design, the greywater folks, is the best available and has good drawings. With this and help from my friend, we were able to build one at Gus’ place.

Standard septic system with infiltrator leach field. Photo by Topanga Soils and Septic

Septic Systems

In your average septic system (see diagram above), the waste and water is flushed into a septic tank where it sits, decomposes anaerobically (septic comes from the Greek meaning “to rot” or “rotten”), and drains into the subsoils. The tank has an overflow opening where waste water, or effluent, flows out when the tank fills up, because solids go to the bottom and liquids to the top. This effluent goes into a drain, or leach, field which uses perforated pipes or, more commonly nowadays, many infiltrators on a bed of gravel to spread the effluent around a couple feet beneath your grass.

The idea is that the effluent is purified by the soil and microbes as it makes it way down to the water table or is utilized by plants above. A new system might cost about $5,000, will have to be pumped out every few years and will limit what you can plant on the ground above it (check out this primer from Virginia Tech).

How to Build the Watson Wick

The Watson Wick System takes a plumbed flush toilet and directs the goods through 3-inch ABS or PVC pipe directly into an infiltrator (or several) with no septic tank. In this system the infiltrator sits on top of a bed of pumice rock — the “wick” part of the system — on grade, not buried below the surface.

The one we installed used about 25 feet of 3-inch ABS to get out and away from the house, about 8 bags of pumice from the local hardware store, and one 4-foot infiltrator (our friend in New Mexico uses two infiltrators). Total cost was about $350.

First, we cut a hole in the bathroom wall that was high enough so a 3-inch drain pipe could make a right-angle turn from the bottom of the bowl and out the wall. In this case, it raised the bowl almost 11 inches above the bathroom floor (see photo). We ran ABS pipe from the toilet to our drainage and wick area.

Raised toilet going to Watson Wick system.

Next, we dug a hole 18 inches deep by about 10 feet long and 6 feet wide. At the high end, we poured out the pumice on which we set the infiltrator. The hole started about 10 feet from the house and we made sure it sloped downward and away from the house.

Then, we made a permeable barrier out of rigid foam insulation (we happened to have a sheet sitting around) by drilling many holes in it and set it upright in a couple feet from the infiltrator. We filled the rest of the hole on the other side of the barrier with lots of woodchips. The pumice was pricey, and we thought wood chips would serve for the secondary wick.

Fourth, at the low end of the woodchip section, we dug out a 1-foot-wide drainage trench that ended near some un-irrigated trees in case of overflow from the wick.

Last, after tying in the pipe to the infiltrator (it just slides into a hole on one side) we covered it with soil, woodchips and dirt. We added a “cleanout wye” along the run for potential clogs, too.

Infiltrators are used because they have thousands of tiny holes along their curved surface that let air permeate but keep bigger particles, like dirt, out. This allows the poop that’s flushed into the infiltrator to compost aerobically on top of the pumice and under the roof of the infiltrator, thus creating a healthy microhabitat rich in beneficial microbes, earthworms and other decomposers. The liquids drain through the pumice and out to the woodchips and adjoining soils where they are purified by microbial action.

Infiltrator with cap and punch out holes for pipe. Photo by The Septic Store

Maintenance and Function

There have been zero issues since the install nearly two years ago. No smells, no backups, no excess water. We took a look into the infiltrator through a little inspection port using a headlamp and the first thing we saw were earthworms frolicking atop and within the pile of goods. Our hearts soared.

Gus has cleaned out and replenished the woodchips once in the two years he’s had the system in operation. They break down over time and make a good mulch for his trees giving another useful input to help his plants and soils flourish which would be lost in a standard system. He also commented that in this process he cut back a lot of roots making their way toward the pumice field which is probably a good thing for long-term system functionality.

After the install, he also added gutters to his nearby roofs to divert rain runoff away from the system so that it doesn’t get overburdened from a heavy rain.

When I last visited, there was a thriving forest of nettle and currants and gooseberries around the wick and milkweed and sunflowers on top of the wick and infiltrator. It was a glorious example of permaculture design principal Number 6: Produce no waste.

The system helps Gus transform urine and poop — what are normally considered waste products — into rich resources, right on their own land. It’s an elegantly simple, slow and local, inexpensive and democratic (accessible to all) solution. And, maybe as importantly, his bathroom no longer grosses out his visitors.