Plans for Installing a Greywater System
Hi all, I’m wondering if anyone has installed greywater drainage systems before, or has any opinions on best practices.
My plan is essentially a parallel drain system, where blackwater (toilets and kitchen sinks/dw) flow to the septic tank, and greywater (everything else) flow to a mulch basin.
My local planning dept has adopted UPC 2021, and Washington state dept of health has drafted guidelines for greywater systems. Both require a 3-way diverter valve (downstream of fixtures/vents) so that greywater can flow to the septic tank when necessary (ie, when the ground is frozen). I plan to install drain pipe and diverter valve so that I am “greywater-ready”, but delay construction of the required sub-surface irrigation system. This should simplify the inspection period.
1. I can’t find a list of ‘approved’ diverter valves, and the only 3-way valves I can find are 90 degree turns. Wouldn’t this slow down the flow too much as it enters the main septic drain and cause clogs? An alternative plan would be to install the diverter valve further upstream, within the vertical portion of the parallel drainpipes…but this would mean the valve is not downstream of all the fixtures. Is this a potential problem?
2. Ive read that low-flow toilets may benefit from faster flow (thus a smaller drain pipe). Given that the greywater drain is robbing the (150’ long) septic drain pipe of even more flow, and considering my low dfu’ s, I’ve reduced the building drain/septic drain pipe since to 3”. Does this seem appropriate?
3. Any comments on my amateur plan are welcome.
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