Slow draining basin

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Malibu Jim, Sep 7, 2012.

  1. Malibu Jim

    Malibu Jim New Member

    Oct 18, 2007
    About 1 & 1/2 years ago, we had our bathroom renovated and the company doing the work replaced the wash basin, among other things. Since then, it seems our sink is sometimes slow to drain. While running water in it, it will drain OK, then suddenly stop draining until it's 1/2 to 2/3 full, then drain again normally. I don't believe it's a venting problem, since it was OK previous to their work. I have taken the trap apart, but never found "anything" in it. I did notice, that it appears, the drain pipe from the sink attach to the connection at the sheet rocked wall is a little smaller than the pipe in the wall. Could this create some kind of a vacum problem ? The sink has never come close to overflowing, but it's just annoying.
  2. kreemoweet

    kreemoweet In the Trades

    Sep 7, 2009
    Seattle. WA
    There is nothing improper about using a larger size drain in the wall, nor could it cause slow drainage. It would appear there is some kind of intermittant
    partial blockage in the pipes downstream from your lavatory. I doubt anyone not on premises will be able to tell you what it is.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    What does the drain in the sink look like? If it's a grid drain with small holes, does the sink doesn't have an overflow? Sometimes, with sinks like that, it gets airlocked, sort of like when you put your finger over the end of a straw...the water won't flow out.
  5. nestork

    nestork Janitorial Technician

    Aug 5, 2012
    It's a clogged sink overflow drain.

    I'm with Jadnashua on this one.

    I regularily have to clear the overflow drain on my bathroom sinks to keep them draining properly.

    But, I don't think it's an air LOCK issue. From what I can see, if the overflow drain is clogged, then when you pull the plug on a full sink of water, the air that was under the plug gets compressed under the clog in the overflow drain.

    As the water drains out of the sink, the pressure on that compressed air diminishes and it starts expanding into the sink drain, thereby pinching off the water flow. Watch closely, and if you see the drainage rate slow to a crawl, and then see a big bubble come out of the drain, and then the sink drains quickly again, it's definitely a clogged overflow drain.

    I have a special 1 1/4 inch trap adapter that's cemented directly into a removable cap. I put a 5 gallon pail under the sink, put a board across that pail, and then put that special adapter on the sink drain, and tighten the nut at the top so it doesnt' leak. Then I fill the sink full with water until the water covers the overflow drain and plunger the sink. Since the water can't drain, the water surge goes through the overflow drain, and I end up plungering all the rotting putrifaction in the overflow drain into the sink through the overflow drain hole. Then I remove the board, take the removable cap off the bottom of my trap adapter and the water and crap in the sink drain into my pail. Then I'm good for a long time again.

  6. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    If it is a vessel sink without an overlow, it will airlock until water starts flowing good, but if the faucet is left running, the aerated water WILL restore the air lock before the sink empties.

    Last edited by a moderator: Jul 21, 2016
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