What's up with this laundry tub drain?

[In-Depth]

This laundry tub drain doesn't look right to me, would this be considered an S-trap? A vented S-trap?

Please enlighten me!

Thanks, Jim

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[kurt]

Where's that branch go? It looks like a vent.

[In-Depth]

Where's that branch go? It looks like a vent.

Yes, it is a vent.

[Marc]

From the 06' IRC

P3105.2 Fixture drains. The total fall in a fixture drain resulting

from pipe slope shall not exceed one pipe diameter, nor

shall the vent pipe connection to a fixture drain, except for

water closets, be below the weir of the trap.

What is shown in the OP's photo is a vent connection that's below the trap weir. This is permitted only on toilet fixtures which is necessary since the trap is integral to the toilet fixture.

Marc

[Tom Raymond]

So it's not allowed by code, but what exactly is going to go wrong with it? I can imagine it gurgling a bit and the vent will flood in a back-up, but so will any other vent connection. The intent of that cite can't possibly be to prevent a noise?

[Marc]

So it's not allowed by code, but what exactly is going to go wrong with it? I can imagine it gurgling a bit and the vent will flood in a back-up, but so will any other vent connection. The intent of that cite can't possibly be to prevent a noise?

Properly vented fixtures don't gurgle. It might work fine but I'd be concerned that suction developed at the weir might pull the trap dry, especially if drain action starts with a lot of water sitting in the basin. Venting relieves that suction.

Marc

[Tom Raymond]

Siphon is the commonly cited 'problem' with S traps but in practice it rarely happens. If all three of those basins were filled and then drained simultaneously, there would be a large slug of water on that line initially, likely recurring a couple times as they emptied, but not at the end of the cycle when it could siphon. It's even less likely since it's vented, wrong side of the weir or not.

I guess I want the 'this bad thing will happen if you don't follow the code' reasoning behind the cite, 'because I said so' was never a good enough reason in my book.

[Chad Fabry]

The vent doesn't do anything if it's on the wrong side of the trap.

[kurt]

It's not on the wrong side of the trap, is it? Vents should be "downstream" from the trap, but not lower than the weir.

I can imagine some hypotheticals, but pretty far fetched.

[Tom Raymond]

It's on the wrong side of the weir.

I can imagine why that's bad design but not why it's bad building practice. The code is not a design manual so I was after why that was the latter. Apparently no one knows.

A basin with an occasional belch doesn't bother me all that much.

[Marc]

Tom, take a look at the OP photo: the vent connects on the discharge side of the trap. It's not on the wrong side, just too low.

Marc

[Bill Kibbel]

My old plumbing design books show vented s-traps were standard for quite some time. This illustration is from a 1910 publication.

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[allseason]

Did it drain well or did it gurgle and make noise? And that is all new pvc so would not the s-trap be something to call out?

[In-Depth]

Did it drain well or did it gurgle and make noise? And that is all new pvc so would not the s-trap be something to call out?

Thanks for the input everybody. The laundry tubs drained well, and there was no gurgling or unusual noises. The clothes washer drain was on the other side of the room, so there was not a large volume of water going through this drain regularly. I wrote it up as the vent was improperly located below the weir of the trap per Marc's reference, may need correction if it causes problems with the drainage.

This was permitted work, so the city inspector passed it, or more likely, didn't look at it.

Jim

[Chad Fabry]

Tom, take a look at the OP photo: the vent connects on the discharge side of the trap. It's not on the wrong side, just too low.

Marc

Yeah, my bad choice of words added to the confusion. It's too low. God forbid I read all the responses before I post.

[Jim Katen]

The thing in the picture is not an S trap. S traps are a type of manufactured fitting. They no longer comply with the codes, but they're real fittings.

The thing in the picture is an improvised mess. Because of this, no one knows how it will behave or what it will do. Unconventional things behave in unconventional ways.

That mess is analogous to a pier made up of Jenga blocks or a maze of electrical wiring with open splices. Sure, it works in the sense that most of the water eventually goes where we want it to go, but that's about it.

Maybe it will never burp or suck its trap dry, or maybe it'll only do it sometimes. But why should we or our clients tolerate that when the knowledge and ability to do it right is out there and within easy reach?

Modern plumbing has pretty much conquered typhoid, cholera, & dysentery, why take a step backwards?

[Jim Baird]

hmmm.

My thinking was an "s" trap is made by a trap arm that is too short...that trap arm was supposed to be twice diameter in length? My check of '06 IRC and IPC does not back up my thinking tho. Seems like I remember it clearly from old '98 CABO.

[kurt]

In my 'hood, that would be widely recognized as an S trap, even by the local 130 fellows. I'm not sure the definition is as hard lined as Katen implies, but I'm willing to call it whatever anyone wants.

It does imply that the installer worked harder than necessary to get it wrong. Although, if you look it over, how would one get the vent in the tailpiece area without pushing the weir down to the floor? I don't think the elevations would allow getting all the fittings in place.

They could'a just ran the trap arm over to the side of the tub, gone vertical with the vent, then brought it all back over to the drain hub, thereby keeping the vent above the weir, but it would've looked even loopier than this job.

Since they were apparently unwilling to get rid of the old "stone" laundry tub (and who wouldn't be?), they did what's going to work OK.

I'd probably report it simply so my folks didn't hear it from someone else.

[plummen]

S-trap,it should be against the law to sell that nasty purple primer to home owners or handymen! [:-censore