a vessel with no overflow not draining fast enough. in this very specific case, i think it is good to point out that "venting" could mean before or after the P trap. In plumbing, venting means after the P trap. If you had two vessel sinks (each with no overflow) connected by a "continuous waste" onto a single P trap, they would both flow well, as air in the pipe below one sink before the P trap would get displaced into the pipe of the other sink. Newbies, search on "continuous waste" to see images. Continuous Waste Center Outlet is easiest to visualize. Continuous Waste End Outlet is the other option. If someone else more qualified wants to add to this description, please do. To add more precise plumbing terms to describe the two kinds of venting. Before the P trap and after. Water and air have to be exchanged (displace each other) for a pipe to drain well. When it drains slow, one can increase the pipe size (which allows air in the pipe to move around the water coming down) by one size, or give the air another place to go to. AAV Studor type valves are for letting air in, not for letting air out. They are used after the P trap not before. Following the logic of air displacement described above, one way to solve the slow drain is to Wye in a standpipe which would then let air move out of the way (get displaced) when water comes down the drain. The standpipe could be hidden from view; it doesn't have to be in the bathroom if you have a more appropriate place for it behind one of the walls. HTH !

lisa- The overflow in a sink has one function: to handle an overflow if the water level gets too high; it has no role in relation to the drain functioning properly. Any properly installed sink drain consists of two parts: 1) the pipe from the bottom of the sink to the P-trap and then on to the sewer, and 2) the vent pipe (usually in the wall) that is connected to the drain pipe and admits air so that there is no suction effect when a large volume of water is going down the drain. If there is no vent, or if the vent gets plugged up, then the water running down the drain tends to cause a suction effect and the water drains slowly. Conversely, if a sink is properly vented, it doesn't matter whether it has an overflow or not. Does that make sense to you?

just wanted to follow up. I tried plunging again for quite a while to little improvement. I tried foaming pipe snake per my usual course along with good flush and more plunging. No noticable improvement. Anyway I went out to Lowes and Home Depot to check out what type of snakes etc they had. I had once attempted to snake it with a borrowed attach to your drill snake. Between it being a dumb snake design and me not being able to get it further than a foot into the tail of the drain I pretty much figured snaking wasnt possible and I hate wasting money. However after years of plunging every few weeks to restore minimal flow I was ready to take a $13 risk and I got a snake from home depot. See my theory was that with sufficient water flow and plunging I could clear most stuff. Well I was wrong. The new snake was a better design for the sink , one of the $13 steel housing hand crank models. Got it into the tail .. still had problems getting around a bend about a foot in but was able to get into the pipe this time hit what I thought was more bends thought I got snake caught at one point. However I ended up with a snake with coating of black gunk along with some very hard pieces thatended up caught in the small coil head. It looked like carbon or graphite almost. After a number of times running the snake back through (all 25' of it) and not pulling anythhing out really. I put everything back together and the sink drains like a champ now. Turn the water on full and it all goes down, no back up. WOW. I'm so glad somthing finally worked. I have no idea what exactly has been building up but I think I've at least puched a significant hole in it, or I punched a hole in my pipe. So perhaps someone can learn from my mistake. Get a snake. Use it. It will probably fix your problem.

First things first. Do not pour drain cleaner in it,,,,,,of any kind. All pop up stoppers I've seen can be removed from sink for cleaning drain. Either find the instructions,go back or call where you bought it or call a drian cleaning service. If you don't mind getting your hands dirty,set a pan beneath it and remove the trap. Don't know how to remove a trap? This is how