Bath Drain Remodel

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Mrosenb

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I'm remodeling the bath and replacing the tub drain. I'm concerned about not replacing the cleanout and about the length of the pipe. I understand there is a max length. Here are some photos of the original and a dry fit of a new p trap. Thats a 60" alcove. Am I doing ok? What should I do?
Thanks!

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Terry

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The tub drain should be vented to prevent the trap from siphoning. The vent goes on the high side of the pipe, not below.
A 1.5" trap can go 42" to the vent, and a 2" can go 60" to the vent.

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Paulypfunk

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Don’t worry about the clean out on the p trap. That is such a inaccessible location that one one would ever use it.
-Yes, you do need a vent.
-According to Hoyle, UPC wants bathtub drains to be 2” in diameter. I understand that might be a difficult undertaking.
- You should connect that bathtub to the p trap, then to a vent, with the vent pipe tying into the drain on the top side of the pipe, so crap can’t collect in the vent to block flow of air. If you can’t get a natural vent all the way through the roof or connected to another existing vent you could consider using an AAV. You can’t just bury an AAV in the walls though. I think it wise to put the studor vent above the flood rim of the fixture. You could stick it in an attic or put in a louvered box to provide air and access. You can put them in a low visibility spot, like the back of a closet or hang a picture over the grill plate.
 

Mrosenb

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Thanks. Although I'm still having trouble figuring out where I connect the vent. The drain pipe is along the bottom of the tub. I picked up an aav and a t connection. I can't use a t or 3way because of the 90 degree, correct? What fittings do I use? I was thinking I could have the vent come out where I marked here next to the supply lines while still being under the tub. It won't be in the wall, there's an access from the closet. But I don't know how to do that. I have minimal space.
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wwhitney

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A few issues: a san-tee can't be used on its back/side like that for drainage, you would need a combo. But the vent takeoff can't be horizontal. And the AAV has to be accessible, e.g. in a wall box with a ventilated cover.

So basically you need to route the tub drain under a wall (or almost under a wall), so your vent takeoff can be vertical (or at least 45 degrees above horizontal). I believe Ohio follows the IPC, so your 1-1/2" trap arm could be up to 6' long (distance from trap to vent). Or you could use a 2" trap with a trap arm up to 8' long. In both cases the total trap arm fall can't exceed the pipe diameter, so to achieve those lengths you need perfect 1/4" per foot fall on the trap arm.

Seems like you have two options: change the elbow at the top of your first picture to a san-tee, if you can get a vent pipe from there into the wall without going horizontal (staying at least 45 degrees above level) and without hitting the tub.

Or you can point your u-bend outlet towards the wall right there with the water supplies, point your p-trap elbow outlet parallel to the wall, use a san-tee on its back (allowable under the IPC) for the vent take off, rolled 45 degrees off vertical, with the vent hitting a 45 under the wall to turn vertical, and then a long turn 90 to turn back towards the existing galvanized drain. Getting that all to fit in the joist bay may be challenging and may require the use of some street fittings. Plus you might need to move the water supplies out of your way.

Probably the second option is simplest/best if it will fit, and if you have a place in that wall for the accessible AAV vent box, or if you can run a dry vent up into the framing above (or attic) to connect with another dry vent.

Cheers, Wayne
 

Paulypfunk

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It doesn’t have to be a santee, although that is the most commonly used fitting. You could change that to a wye fitting on its back as long as the drain goes straight through the fitting and the vent attaches to to side of the wye. The barrel of the vent must be rolled up enough so the vent is dropping into the top half of the pipe. I know you are fighting for the slope so the closer you can get this vent connection to the side or end of the tub, the easier time you will have. That location for the AAV has to be accessible. You can’t seal it into the drywall. I also like to extend them above the point where water will spill over the top edge of the tub, the “flood rim” as we say in the parlance of our times.
 

wwhitney

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It doesn’t have to be a santee, although that is the most commonly used fitting.
Yes, a wye or combo is generally a better choice for a vent takeoff, all other things being equal (and is required by the UPC). I suggested a san-tee on its back because it's more compact and I expect space in that joist bay would be tight for the trap elbow, san-tee, and LT90 to all fit in a row.

Cheers, Wayne
 

Mrosenb

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Ok what I understand is something like this. I’ll have to push this back farther and drill a hole into the baseplate. I’ll also make the aav higher. Accessibility shouldn’t be a problem as this isn’t getting covered up. Second photo is from inside the adjoining closet.
Does this look better?
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wwhitney

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Yes, that will work.

You could roll the san-tee 45 degrees and stick a 45 (possibly street) on the vent takeoff to get back to vertical. That would get you farther back. It's fine to notch the base plate as required.

Also, if you make the san-tee street (or the LT90), that might help you avoid the water lines.

Is your trap inlet going to end up in the right place?

Cheers, Wayne
 
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