Slow bath sink drain

I installed two new vanities and sinks during a remodel. The drains are run through seperate traps and seperate drains in the same drain run. The vent pipe runs parallel above the drain run. The vanity and sink heights are different, 30 and 36 inches. The lower sink drains well, but the taller sink drains much slower, bubbles form in the sink strainer and appear to block the flow. If I run my fingers across the strainer it runs faster, when I stop, the flow slows. Any ideas? Vent problem?

drain

It appears you have a "grid" strainer and the openings are too small to allow air to escape while water is covering them. Either drill the openings larger or install a different type drain.

Thanks for the reply. Why would one sink with the same strainer work well, and the other not?

Does one have an overflow and the other doesn't?

drain

Both basins are hand thrown and do not have overflows.

with an overflow, water can start flowing without meeting much resistance from the column of air in the pipe, since a small volume of air can be displaced into the overflow space to give room for the incoming water. With no overflow, you have to displace air and water inside the pipe walls. Maybe your second sink is too perfectly installed, so air and water end up in equilibrium. Unbalance that strainer. Some air has to come out to leave room for water to go into.

Seems to me that if everything is the same between the two setups except for the one difference, then you have a scientifically valid example of having met up against the limiting factor. But I doubt that is the case. Too many things could have changed between the two. Look hard at the one sink that does drain well and see if anything is different. For example, maybe it is slightly unlevel and that lets water go down more on one side while air escapes more on the other side of the drain hole. No kidding.

David

Drain

Thanks geniescience,

I think you hit the nail on the head. Last night I turned the faucet on and let the sink fill. When the sink was 1/3 full, the water drained out very quickly and continued to drain well until I turned off the faucet. Any ideas on a solution short of replacing the sinks?

any way that will unbalance the perfect symmetry with respect to the gravitational axis. At the opening. Perhaps a hole drilled or punched in the straincover at one side. I'd punch it since that would make a small depression and that my good man is what that drain cover needs.

David

"Your installation is too perfect; you must be Hungarian" -- H. Higgins