Parallel drain system for greywater - pipe sizing

[AdamPNW]

Hi all. DIY installer of a greywater DWV system in Bainbridge Island (UPC). Iso drawing attached. Im trying to size the greywater to a 2” drain pipe since the recommended 3-way pool valves are 2” (And it seems 3” 3-way valves would be prohibitively expensive). Diverter valves to an approved septic system are required here.
The problem is when the 2” greywater drain becomes horizontal, it no longer can accommodate 14 DFU, per code. Can a 2” drain pipe be split into two 2” pipes before it becomes horizontal? of course, then each section would need to be diverted, but possibly this is preferred over a large 3” diverter. Thoughts?
thanks, Adam

 

[AdamPNW]

Anyone have any thoughts about this greywater parallel drain system?
thanks!

 

[Sponsor]

 

[JoeJee]

Yes, you can split it up and have two separate lines that tie into the 3” assuming all else meets code. I don’t know how restrictive those valves are for DWV non-pressure so can’t say if your idea is good or not.

 

[Jeff H Young]

if you are talking about taking a single 2 inch drain line on the down hill side splitting it to 2 no you cant

 

[wwhitney]

Can a 2” drain pipe be split into two 2” pipes before it becomes horizontal?

No, you can't do that.

What you can do is to avoid creating a vertical 2" pipe with more than 8 DFUs in the first place, by keeping the fixtures separate. So you'd have two parallel vertical 2" drains, each with no more than 8 DFUs.

Cheers, Wayne

 

[John Gayewski]

You can definitely split the two sections and keep them seperate until after your diverter.

This is not a thing I've dug into. I'm not sure a pool diverter valve is OK for this. I'm actually questioning any type of system that diverts drainage. As the code has sections that would contradict the possibility of diverting. If the system needed changed later I don't think valves are a feasible way to merge a gravity drainage system. A pumped system could divert and re-divert sure, but gravity systems generally (at least in the past) aren't for changing back and fourth.

 

[wwhitney]

This is not a thing I've dug into.

See UPC Section 1503 for gray water systems.

Chapter 15 Alternate Water Sources for Nonpotable Applications: Alternate Water Sources for Nonpotable Applications, Washington Plumbing Code 2021 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne

 

[John Gayewski]

See UPC Section 1503 for gray water systems.

Chapter 15 Alternate Water Sources for Nonpotable Applications: Alternate Water Sources for Nonpotable Applications, Washington Plumbing Code 2021 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne

That link doesn't show anything beyond the first coupe sections. I'll probably have to look at the actual upc version