Lowering P trap for tub drain clearance...?

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J Blow

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I'm replacing an old standard tub with a 2 piece freestanding tub so purchased a Maax F2 drain system where you install a receptacle type piece in the floor where you can leave a tailpipe like piece on the tub and just drop it into the drain.

My problem is that this unit, where it connects to the P trap under the floor, is now a few inches lower than the drain line. Usually the drain line 90s to the p trap, which sits below the tub obviously but I'm needing to add a few inches down between the 90 and the trap which will make the trap about 3-4 inches lower than the drain line than it was before. Doesn't seem like it would be a problem but maybe I'm missing how it changes, the pressure, flow rate, etc...?
 

J Blow

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Maybe a picture is worth a thousand words... Is this ok?
20230305_175822.jpg
 

wwhitney

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Maybe a picture is worth a thousand words... Is this ok?
No.

(1) I don't think you can use a u-bend and a vent-tee to make a trap. (2) The trap seal depth, the height between the red lines in the markup I did below, needs to be in the range 2" to 4".

So you either need to figure out how to raise your trap, or you need to lower the requisite drains.

Cheers, Wayne

20230305_175822.jpg
 

Jeff H Young

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Ive seen them with maybe a inch between the hubs but not like that. I dont really do installations like that so cant guess how well it would work obviously water will go through there but long term who knows how much you can get away with Im not sure of the maximum trap seal permitted. BTW the return bend is backward ( pet peeve)
 

J Blow

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No.

(1) I don't think you can use a u-bend and a vent-tee to make a trap. (2) The trap seal depth, the height between the red lines in the markup I did below, needs to be in the range 2" to 4".

So you either need to figure out how to raise your trap, or you need to lower the requisite drains.

Cheers, Wayne

View attachment 91159
If I'm understanding correctly, this is ok as long as the area between the 2 red lines is less than 4"? Right now it's exactly 4 inches and I do have room to cut it down another inch or so.

Thanks!
 

J Blow

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Ive seen them with maybe a inch between the hubs but not like that. I dont really do installations like that so cant guess how well it would work obviously water will go through there but long term who knows how much you can get away with Im not sure of the maximum trap seal permitted. BTW the return bend is backward ( pet peeve)
Right now there's 2 inches of pipe in there... I'm pretty sure I have room to cut it down to one so I think this will work. Thanks!
 

J Blow

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No.

(1) I don't think you can use a u-bend and a vent-tee to make a trap. (2) The trap seal depth, the height between the red lines in the markup I did below, needs to be in the range 2" to 4".

So you either need to figure out how to raise your trap, or you need to lower the requisite drains.

Cheers, Wayne

View attachment 91159
Also, point 1 noted.

Thanks.
 

wwhitney

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So the tub should dump into the right side of the u bend and drain on the left?
No, he's referring to the way the u-bend itself is not quite symmetrical, if you look at the two "corners". The fixture drains into the left and out the right in your picture.

As to modifying a u-bend to increase the trap seal, not sure if I would do that, but if I had to, I'd be inclined to use the parts provided and flip the elbow around, so the street end is the outlet. Or maybe stick a very short segment of pipe and a coupling between the u-bend and the outlet elbow.

Cheers, Wayne
 

Jeff H Young

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people put the return bends backward all day long every day i dont think it matters much or at all perhaps, just wrong
 
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