How to plumb double sink 48" vanity?

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Midwestboy

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I'm stumped. I've read don't use 2 p-traps with less than 30" between sinks or I'll have issues with slow-draining, mold, etc. Preferred method is a Tee to one p-trap. But in this short vanity with drawers both in the middle and the bottom I can't seem to navigate enough room to do it inside the cabinet.

Would it be ok if I run a p-trap for each sink out the back of the vanity to their the common waste line branch (giving me 30" between waste line entry points)?

If I did the proposed 2 p-trap solution, would I be safer to add another branch vent to the waste stack as shown in attached drawing?

The alternative seems to be some sort of rinky dink 1.25" plastic pipe from the hardware store somehow mated for a side exit with one p-trap. Those didn't look like they'd drain very fast. Right angles, small diameters...

Any advice appreciated.
 

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WorthFlorida

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There is no issue with two p-traps and distance minimum is as long as the trap arm is of the proper length. A 1-1/2” pipe would require a 3” minimum trap arm. This is my home done a few years ago by a licensed plumber for both Florida and NY State. It was a single sink with an AAV. One AAV handles it just fine. MO is UPC which AAV's are allowed. My AAV is in the wall cavity and the wall was not closed in. There is easy access on the other side of the wall. Zero issues with draining.

1664999962625.png
 

Midwestboy

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Thank you!

Your pic has vent inbetween the drains. I was just concerned that without the additional vent, the water coming down the left sink into the waste branch drain would suck the water out of the p-trap of the first drain, or water from right sink draining would try to pull air from left sink and drain slowly as well.
 

Tuttles Revenge

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The reason they don't cross over and suck the other trap dry is because they have enough distance and slope between each trap arm of the double fixture cross fitting. Its specifically Not a double San Tee which can have that problem. But that configuration requires a 2" drain to combine 2 fixtures together.
 

Mr tee

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I would use a 2 X 1 1/2 X 1 1/2 X 1 1/2 double fixture tee with a 2 LS 1/4 under it that runs to the stack. I assume that stack does not act as vent for something on the floor below because that would not meet code. The double san tee shown in the picture above is a poor choice because if you ever need to snake the drain the cable would go down one side, across the double san tee and up the other side.
 

Midwestboy

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I would use a 2 X 1 1/2 X 1 1/2 X 1 1/2 double fixture tee with a 2 LS 1/4 under it that runs to the stack. I assume that stack does not act as vent for something on the floor below because that would not meet code. The double san tee shown in the picture above is a poor choice because if you ever need to snake the drain the cable would go down one side, across the double san tee and up the other side.
"2 LS 1/4 under it"
what is that?

You'd take out the horizontal branch waste line and replace it with at 2" branch waste line starting below the double fixture tee, is that right?
 

Reach4

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LS= Long Sweep (bigger radius 90 for drainage). You can also uses two 45s instead of a long sweep.
 

Jeff H Young

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not so sure the image shows a double santee or double fixture fitting but use the latter
 

Reach4

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Thank you!

Your pic has vent inbetween the drains. I was just concerned that without the additional vent, the water coming down the left sink into the waste branch drain would suck the water out of the p-trap of the first drain, or water from right sink draining would try to pull air from left sink and drain slowly as well.
Lack of venting after the trap does not cause slow draining on its own. The primary purpose of the venting is to prevent the trap from siphoning out. With a big pipe belly, it is possible that a vent can be improve draining, but a big drain pipe belly is not common.

What can surprisingly cause slower draining in a lavatory is to not have an overflow for the lavatory. This is common with vessel sinks. An overflow keeps pressure from building up between the stopper/grill and the input to the trap.
 
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