shared plumbing trench

I have a detached garage that serves as my woodworking shop. My latest project involves installing thermal solar collectors on the shop roof and piping the hot water back to the house provide heat for the domestic water heater.
Part of this project will involve a 40' trench from the shop to the house for the solar heating pipes - hot supply and cold return. Currently the shop does not have any plumbing. I was thinking that while I've got the trench open I could run a water line from the house to the shop and and a sewer line for a utility sink.
Altogether the trench would have:
2 insulated pipes for the solar heating system 1 cold water line to the shop from the house 1 sewer line from the shop to the house
I should add that the floor of the shop is slightly above grade and the pipes will be run to the house basement, the floor of which is about 5 or 6 feet below grade. I only want to install one utility sink in the shop; no toilet.
My questions:
1) Is this shared trench a massive code violation in the US? (located in VA) 2) What is the smallest sewer/drain line that can be installed in such a scenario? I have an ideal location to tie into the house's sewer via a 3" tee 3) IIRC the drop for a sewer line should be 1/4" per foot - is this about right?
Thanks for any help you can provide!
Eric
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wrote:

Eric, since noone else is answering, I'll take a stab at it. I'll warn you, I'm no expert, but have picked up some things as a contractor working with excavation subs.
A shared trench is not a code violation. water and sewer is regularly run in the same trench. I believe they have to be three feet apart. I doubt if your solar hot water lines would be governed by code.
Don't know the answer to number 2. Seems like would be governed by plumbing code as it applies to the plumbing in your shop. (My current project has a forced main, and that has a 1 1/4" sewer line!)
I believe the slope in a buried sewer line can be as little as 1%. Don't quote me on that either. I know it is less than 1/4 per foot though. Course that is the slope from the house to a city sewer. Yours is a different situation.
Do you have a building department you can call? That would be the best place to get some answers.
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There is no U.S.-wide plumbing code that I'm aware of. Particular to VA, not sure.

Standard drain pipe is 4". Don't use DWV underground.

That will drain the liquids in the line without leaving too much sediment behind.
--
Dave

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Perfectly OK. Be sure and follow your city's code for burial depth if it is a freezing area.

It's really just a lateral for a single fixture. I wouldn't use anything less than 2", although since it is a separate building, I bet code would require that it be a main, 3". Be sure and add a vent in the garage for the sink, especially with such a long run. Under the sink you will have a trap, then tee in on the house side of it and run 2" through the roof.

That's correct.
One other thing: be sure and slope all lines back towards the house so you can drain them if necessary.
--
Dennis


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Thanks to everyone for your responses and assistance. It sounds like my approach is feasible enough to talk to the local building officials.
Thanks again,
Eric
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No problem other than meeting separation distance both height and width. Contact local AHJ.

If there will be solids (crapper?) 3" will be the minimum.

3" pipe will require 1/4"/ft fall.

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