Grey Water – Tank Size and Piping
Hello All,
Working on the plumbing for our 2100 sq ft house. We’ll be on a septic system and I was reading up on the do’s and don’ts of septic. I found that it is best to try and keep the lint from the clothes washer out of the septic tank and leach field. That makes sense to me. So, I was doing a little research and found that there are lint traps for the water line that we could use. We are building in the high desert of Idaho and the plan was always to capture rain water off of the metal roof. But it makes sense to me that we could just route the washing machine drain, a couple of sinks, shower and tub to a separate holding tank.
In affect I’d have my septic system on the east side of the house and, since the washer is closer to the west, we capture grey water on the west.
The attached image is part of the Site Plan and shows the septic, well, domestic holding tank, proposed grey water tank and grey water devices (sinks/washer).
Does anyone have experience design a split system like this?
I am sure that it’s regulated by some gov’t agency, but would the hassle and saved water (we’ll be on a well) be worth the effort? Would the grey water pipes just exit through the foundation walls?
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I don't have any knowledge about how bad it is to have lint from clothes washing water go to a septic tank...seems like a common thing.
I do know a few things about greywater though. Please don't store greywater in a tank. It's full of soaps and other stuff that bacteria find interesting...which leads to smells in short order. You're better off sending the greywater out to its final location in your landscape and storing the moisture in your soil, where the biodegradable soaps you'll be using can be broken down. Check out OasisDesign.org or GreywaterAction.org for more information from folks that know.
https://oasisdesign.net/greywater/misinfo/
Thanks Kent. I have heard that some local codes require that grey water only be stored for 3 days. I was thinking of just enough storage to hold on to the tub water (60 gals?) while it waits to sent to the vegetation (gravity for overflow and pumped for other areas).
I'll see what I can find at the links that you've provided.
The idea is that you build your mulch basins large enough to accommodate peak flows. For example, a 2' diameter 2' deep hole (filled with mulch) has a volume of ~47 gallons. Sure the mulch takes up a little space but not much. With a few of those and percolation it works.
Kentthompson,
If you are using mulch basins, is there any advantage in separating the grey water from that going to the septic field?
I am wonder if any architect folks ever build grey water into a residential system....?
Well, it looks like the primary device (clothes washer) that caused me to look into this is specifically excluded as a source of grey water by Idaho.
It does make sense to me to perhaps pursue it for the shower, tubs and sinks....maybe.
Reading that, it sounds like they expect that the water will be dispersed through drip irrigation. A tank is required so that your plumbing doesn't back up if gray water is being produced faster than it can be dispersed.
I have looked into graywater systems several times but the rules are pretty strict here in Maine, and the one time we did use a graywater system it was hardly any different from a regular system. I believe other states have more options.
The critters that live in septic tanks can break down pretty much anything bio-based, but a lot of our clothing (and lint) is petroleum-based. Some of them can be broken down but others (such as those with PFAS and related compounds) last forever.
I went through a similar issue with my home. Grey water sounds good in theory but pretty hard and expensive to get right in practice.
Instead of a full grey water install, I piped the drains separately, this way if it ever needs to be installed, it is simple to add in the storage tank and filtering.