New Sink Drains Slowly

[Darren Sleister]

I had a plumber swap out the sinks in the photos below. Sinks are in the same bathroom and appear to be on the same drain lines. But with drywall that's not 100% certain. Anyway, the sink on the right [1687] drains slow and an occasional air bubble comes up. Sink on the left [1688] works fine. Could this flow difference simply be because of the drain discharge height? Left sink has an additional extender vs right meaning the water is flowing 3-4 inches lower vs right hand sink. Does water velocity matter? Is this a ventilation issue? Would a 2" drain be better? Should I pipe the right sink over to the left with a 2" line? Any idea on how to fix the problem????

 

[Terry]

Each lav needs venting. I can't tell by the picture how yours was done.
Have you checked the vertical lav drain to make sure that is clear?

 

[Sponsor]

 

[Darren Sleister]

Each lav needs venting. I can't tell by the picture how yours was done.
Have you checked the vertical lav drain to make sure that is clear?

Both are vented and I suspect properly so given local building codes and inspectors. I suppose there could be a block in the vent and will have to figure out how to check.

 

[ItsRaulinho]

I lean towards a venting issue

 

[WorthFlorida]

Did the old sink have this problem?

The bubble is a good indication that it is a vent problem, however you can try removing the trap and doing what I explained below. If this sink drain has a pop up check that it is high enough to allow the water to drain and it is about the same height as the other drain. If the pop up is barley above the drain, it will drain slowly.

The sink with the slow drain issue, remove the p-trap and place a pail under the drain. Fill the sink with water and then allow it to drain. If the water rushes down the sink drain assembly, it is OK. Look inside the trap that nothing is in it. If it is all clear then the problem is somewhere past the trap arm.

 

[Reach4]

Lift the stopper out of the slow sink. How is the flow then?

Now a more involved test. Close the stopper in the slow sink. Fill the bowl to the middle of the overflow holes. Run cold water into the bowl at roughly 1/4 of full flow. Does the overflow accept water for a minute? If no, try the same test on the sink that drains well.