Single P trap for shop drains?

[brnctt]

Hey guys, currently my shop has a single drain sticking out as a rough-in, which I plan to connect to two sinks. It exits through the footer and starts its 2% slope immediately. Its about a foot underground.

Instead of installing a P trap at each sink, and then keeping them from freezing in the winter (shop will be unheated), could I instead plumb in the P trap in the pipe underground as soon as it leaves the slab? It would be unlikely to freeze even a few inches below ground, as we only get a few days below freezing a year (mid 20's at the lowest). This also has a benefit of giving me a few inches of extra elevation so I can slope the drain pipe a little more.

The only downside I can think of would be cleanouts wouldn't be as easy. However where the pipe goes vertical after coming out of the slab, I could install a T and have a cleanout pipe coming above grade.

 

[nmk_61802]

I would not bury the P trap, but that is me. If you do, I would move the cleanout ahead of the trap. With your proposal, the vent is also on the wrong side of the trap.

 

[OccupantRJ]

Your winter sounds like ours. My shop when unheated inside maintains above freezing all year round. It is insulated in the walls but not the ceiling. Water supply and drains in the shop do just fine.

 

[brnctt]

The vent would be an extension of the blue line on the left (inside the shop walls).

 

[nmk_61802]

The vent would be an extension of the blue line on the left (inside the shop walls).

Yes, wrong side... serves no purpose there

 

[tarmy]

Put in an oversized drain if you have it in the slab footer so it will be easier to snake if needed. Use a 2 to 3” ABS in the cement.

 

[The Cobbler]

what you;re proposing is called a building trap . here they are not code compliant. and even back int he day when they were common, each fixture was still trapped and vented . your vents will be on the wrong side of the trap .
would it work? probably
would it be easy to clean when it gets full of whatever? nope.
would I do it? nope

 

[Leaflessshadetree]

What is it connecting to after it leaves the building, sewer, septic tank, open air, some type of drain pit?

 

[Innovate1]

There has to be a vent AFTER the trap. Otherwise the water in the trap will be siphoned out. If you are going to do that (and I withholding opinion if that is a good idea or not) you need a vent where you show capped cleanout.

 

[mike93lx]

A p trap freezing won't really be a problem other than making the drain plugged until it thaws. Since it's not contsrained, it shouldn't cause any damage.

Since this is a rare thing, is that a problem?

 

[Leaflessshadetree]

A p trap freezing won't really be a problem other than making the drain plugged until it thaws. Since it's not contsrained, it shouldn't cause any damage.

Since this is a rare thing, is that a problem?

P traps can crack or when the water freezes.

 

[brnctt]

Yes, wrong side... serves no purpose there

Ah, yes you're correct. I'd have to install a vented cap on the cleanout pipe. Not a problem.

What is it connecting to after it leaves the building, sewer, septic tank, open air, some type of drain pit?

Either a dry well or direct to ground via a popup emitter (after some length of underground pipe), working out which way to go. It's just for a sink but our ground percolation is just about 0 here. Leaning towards ground so I don't have to worry about possibly pumping the dry well if it fills up in the wet season.


To be honest guys most of the reason I'm asking about this is I want that extra 6"+ of head height for drainage. It's about 16" underground right now and I'm not sure I can get to open drain with a 2% slope somewhere on my property. But, I plan to measure this weekend.

 

[Leaflessshadetree]

If direct to ground (ignoring codes, legalities and all that stuff) you might not need a trap at all .

 

[brnctt]

If direct to ground (ignoring codes, legalities and all that stuff) you might not need a trap at all .

How about for a dry well on-site? P traps still good idea?

 

[rlitman]

what you;re proposing is called a building trap . here they are not code compliant. and even back int he day when they were common, each fixture was still trapped and vented . your vents will be on the wrong side of the trap .
would it work? probably
would it be easy to clean when it gets full of whatever? nope.
would I do it? nope

To me, it sounds a lot like what you would find in a commercial kitchen (with a grease trap). That's not residential code compliant, but it has it's place.