Very Slow Tub Drain (Vent/S-Trap)

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KLF

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HI

We are in the process of remodeling two baths one of which has an existing tub with very slow drain (say up to 10 min to completely empty a full tub).

While the city plumbing inspector was out to have a look at the work I have completed in the other bathroom, he commented that there was no vent in the other (slow tub) line and that the S-trap needs to be removed (not my work).

Essentially the tub drains into a standard 1.5" diam. ABS P-trap then runs horizontally over two air ducts then has a pair of 135/45 elbows to zig-zag over and down before emptying into the 4" main line.

The inspector called the zig-zag arrangement an "S-trap" but it is obviously not the conventional type as there is no place in which to physically trap water.

Is the problem really a lack of vent? I assume that the fact that it is emptying into the mainline provides enough air so an anciliary vent is not required.

My assumption has always been that the horizontal run (approx.4') over the air ducts is either unsupported, poorly supported or perhaps negative slope and it is one of these things that causes the poor drainage.

The area in which these pipes are laid is very cramped and I won't have full access until I do some more demo. I would just like to know what the likely cause is so I can starting planning the proper modifications!

I can email a sketch if anyone wants.

Thanks in advance
KLF
 
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KLF

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Here is a sketch of the routing. Like I say, it's a P-trap under the tub then over two air ducts followed by the zig-zag into the main line. The total horizontal run is approx. 5' and the total drop is 10 - 12".
 
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MG

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Does the tub have a popup drain? Unscrew it and see if there is a mass of hair in the drain. Or snake it - there could be a big chunk of hair in that trap. I have two daughters w/long hair and when the tub drains slow I have to clean out the drain. Sometimes the amount of hair that comes out looks like a drowned squirrel.
 

Gary Swart

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I'm not a pro, so let's hope if I err in something, it will be correct. I'd say the lack of a vent could well be a big part of the problem, and all drains need a vent anyway. The hair clog is a pretty good theory too, especially if the tub has drained OK in the past. As a non-pro, I can't comment much about the S trap. Perhaps it is, but I don't see it that way. If in the course of doing the project you could eliminate that and perhaps give a tad more slope, it might help also... sure won't hurt anything.
 

WestcoastPlumber

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According to the drawing, you have your trap arm going over 2 ducts, this is illegal and needs to be changed.

You are not allowed to have anything from the trap to the santee, this will cause drainage issues because the water travels up and down before even hitting a vent and it will siphon the trap. a big no-no

there was mention of the fixture not being vented??? every fixture has to be vented. you need to install the trap and run a 1/4" per foot to the santee. check your code so you know how long your trap arm can extend before dumping into a santee.

and once again, the santee needs to be vented.
 

KLF

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Hi Guys,

Yes the hair issue is a possibility - given that my wife and daughter could both contribute in that respect. We are new to this house (~6mo.) and really only noticed the problem in the last couple of months. However, in our previous house (we were there 8 yrs) we had no similar problem.

The house is 30 years old and I suspect that this plumbing is original and even so, it is not my work. Thus the inspector can't make me alter the plumbing as it is. However, that doesn't mean I won't change it -- I just want to make sure that when I do remod that bath, that I get the lines right!

Westcoast - When you say the "santee" do you mean the 4" main that I refer to? That pipe does extend through to the roof as the main vent as well a going down and out as the main soil pipe to the City line.

If I do reroute the trap extension under the air ducts it would have to be quite a bit lower as (the sketch doesn't show) there numerous other tie-ins just below the one in question. I would estimate that I would have to lower the whole line about 3' to clear the other tie-ins. Where is the best place to add the vent tie-in? I would assume right after the discharge end the trap, no?
 

WestcoastPlumber

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the trap arm needs to remain at a 1/4" per foot to the tie in, or santee, or stack, yours being 4"

You cannot drop or raise a trap arm in any way.

if you need to go under, then go under, the tailpiece connecting to the w/o, which is the verticle part can be long.

just don't drop or raise the waste arm, it must remain 1/4" per foot to the verticle tie in.

to bad you are not able to snap pictures, your drawing is nice, but it may be exagerated, it is hard to tell.

either way, the horizontal trap arm must slop 1/4" per foot.
 

hj

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drain

You have a version of a 3/4 "S" trap, but that is not the reason the tub drains slowly. Drains without a vent typically drain better than those with vents, but that is the problem because they work too well and suck all the water out of the trap.
 
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