Slow Bath Sink Drain (No Clog, No Gunk)

[Shaivism]

I searched the forum and other places but can't seem to find my answer. My bathroom sink drains very slowly after a renovation. Originally I had a 31" vanity, but installed a comfort height 36". P-trap is good, sink stop is good, no clog, sink stop is open as far as it goes, pipes are clean and no clog. It almost seems as though I need a vent attached to the drain tail piece. A plumber reviewed my issue and suggested that because the drain tail piece is long at 15 inches, that is why I have my problem. Actual drain tail piece from bottom of sink to bottom of p-trap (bottom of u) is 15 inches. I did not have this problem previously, only after going to the comfort height vanity. Thoughts?

PS. Yes, I know the drain stop rod is unattached in the photo.

 

[Pat the Plumber CIL]

Take the stopper out and put the lift rod back in . See if it will drain then

 

[Shaivism]

The culprit is the Hansgrohe pie shaped wheel on the drain stop. When stopper is removed, drain works. When stopper is installed, that pie shaped wheel near the lever pull eyelet causes a slow drain. Thank you.