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Old 12-16-2017, 06:04 PM   #1
Arch-psyduck
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Default P-trap is blocking my bathroom sink from draining

My bathroom sink has always drained very slowly. Recently the room was renovated and the water continues to drain poorly even though the hardware is all new up to the wall.

While trouble shooting, I found when just tail piece coming down from the sink, the water drains at an acceptable rate. As soon as I attach the P-trap, the water virtually stops draining even if the end of the P-trap is open to the air rather than draining in to the wall's pipe. The P-trap is new and I have inspected it that there is no blockage.

I would appreciate some advice on further steps to take as what I'm observing doesn't even seem to match how water actually works.


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Old 12-16-2017, 07:21 PM   #2
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Post a pic of your set up


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Old 12-17-2017, 04:29 PM   #3
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probably not vented after the trap which can slow the flow.
do you have a grid strainer or a pop-up type drain.
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Old 12-18-2017, 02:12 PM   #4
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It is a pop-up style drain plug. There is no venting along the drain line.
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Old 12-19-2017, 12:45 AM   #5
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Here is the drain. Immediately inside the wall, it turns 90 degrees to the left and connects to the main drain a few further down the wall. The pipe is pretty much completely horizontal.

When it's just the black section, the water drains quickly. As soon as the trap is attached the flow slows to a crawl even if its not hooked into the wall, so it seems to rule out a blockage as the immediate cause.
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Old 12-19-2017, 01:53 PM   #6
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Even with proper venting in the wall after the p-trap I have seen slow drains with pop ups. the pop-plug sits to low and because you don't have an overflow on sink that allows air to follow the water it gets a bit air locked. I found by lifting the plug up a bit it drains faster. how does it drain with the pop plug removed.

Experiment. take a small straw and stick it in the drain with the pop plug in place.
does it drain better. If so that's because the strw is breaking the air lock and allowing air to flow down with the water
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Old 12-20-2017, 01:44 AM   #7
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I haven't had the opportunity to remove or adjust the plug to test the flow.

When I put the straw in the drain, it was amazing; the water actually flowed like it was supposed to! How does one break up that airlock without a straw in the sink? I see options for air admittance valves, but those all seem to attach past the P-trap.
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Old 12-20-2017, 01:22 PM   #8
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you could replace the pop-up assembly with one that has an adjustable shaft. Moen makes one. It's a Brass unit, not that cheap plastic.

Commercial 104770 Moen Pop-up. Plug has a an adjustable brass shaft that you can extend the plug up a bit.
sometimes you can just pull up on the plug a little and it stays up until you bump it or use the lever to close it


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