We had a pedestal sink installed a few years ago. The previous, cabinet mounted sink had no drain issues. This new sink has always drained slowly, then give one burp near the end. Both the plumber who installed it and a second plumber have been unable to solve the problem. The original plumber put a thin plastic straw down the drain, which did not help. The second, non related plumber, snaked the drain, which did not help either. Any suggestions? We are baffled, as the old sink drained fine.
Sounds like the waste stack isn’t properly vented. Any of the other fixtures have any trouble draining?
Did the old sink have an overflow hole at the top of the bowl in front, and the new one doesn’t? There could be an air bubble forming under the drain stopper, preventing much water from flowing out. A way to test this is to remove the stopper completely. If it flows easily with the stopper removed, there’s the issue. I’m not sure how you’d fix it, though.
ETA: I tried to find a picture, in case the part about the overflow was confusing. Here’s a pedestal sink with the overflow hole just below the faucet. The ones I’ve seen are on the side opposite the faucet, but maybe with a pedestal sink that’s not an option.
Have you pulled apart the tailpipe assembly and p trap?
It should be easy to isolate if the problem is proximal or distal to where the drain enters the main plumbing stack. Snake or not that’s what I would do. Sounds like the straw guy was venting the sink grate which can sometimes trap air bubbles if the holes are too fine. I doubt that is the cause.
The overflow pipe drain is unlikely to be the cause, present or not. On the other hand the main plumbing stack vent is not a likely cause since it used to drain well. So I woild start by figuring out if the cause is proximal or distal to where the sink drain joins the main plumbing.
I have a slow drain in my kitchen. After taking it apart, cleaning the trap, snaking the drain, making sure the other side isn’t slow, checking to make sure it’s properly vented, I finally realized that the drain basket is just too restricted. It dawned at me that water backs up almost immediately, as opposed to ‘filling up’ from a few inches or feet downstream.
So that’s something to look at. Does the water have to run for a few seconds before it starts backing up into the sink or does it happen virtually right away. I assume this is a bathroom sink (since you said it was a pedestal), so I would try taking the drain stopper out and running the sink that way. Does it flow more freely that way? If not can you get a feel for where the bottleneck seems to be?
A common cause for slow drains these days is air trapped in the water trap. The “burp near the end” indicates this may be the cause.
If the drain pipe is clear and flows freely and the drain itself is clear and flows freely then the most common problem is air trapped in the trap.
Old drains were cast and had big holes which allowed air to escape into the sink. Newer drains are plate with holes and very often these holes are too small and the air is trapped below and cannot come up. This blocks the water. Holes of 1/2" diameter should be fine. Holes 1/4" or smaller will cause this effect.
In ye olden, classical times the drain was a funnel-shaped cast metal part which was inserted from above the sink and held in place with a large nut from below. Now the drain is a funnel-shaped plastic part placed from below and held up against the sink by a metal plate with holes. The total opening area in the old style was much larger and they drained better.
If the overflow pipe goes to just under the drain then air should be able to escape through the overflow pipe (again, assuming it has a nice cross-section).
Some tests which would indicate this problem:
A small amount of water drains slowly because it cannot push the water out of the way. Filling the sink to the edge will normally have enough pressure to push the air down and the water will drain fast all the time until it is all gone.
When the water is blocked try using a plunger ora syringe or even your hand to create suction which will suck the air bubble out and allow the water to flow. Or you can use a straw to suck the air out. If this solves the problem then it is caused by air trapped.
Possible solutions are:
- Put a drain plate with bigger holes or enlarge the existing ones so air can escape. Or, best of all, get an old style drain which was all open. Even without air problems these drain much faster because they have much greater open area.
- Provide an exit for the air in the trap. The overflow pipe is supposed to do this if it is correctly designed.
- Remove the trap altogether. This may not be acceptable if sewer gas needs to be blocked but sometimes another trap is installed or can be installed down the line. I did this to the sink in the boat and the difference was astounding. Blocking sewer gas is not a concern there.