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Plumbing in the Home/Upstairs sink drains slow, then fast


QUESTION: I just moved into a single-family home in Colorado, built in 1980.  When I'm shaving at the sink in my master bedroom upstairs, the water drains slowly for a minute or two, so the sink almost fills up.  Then it starts draining quickly.  The sink is empty in 10 seconds and continues to drain quickly for the remainder of the shave.  While it's draining quickly, there is a sort of banging noise every 5-10 seconds from inside the wall nearby.  I guess this is due to a blockage in the vent to the roof?  How do I locate and clear the blockage?  Will there be a point in the basement that I can stick a compressor into or something?

ANSWER: Not a clogged vent and no need worry about basement access. Just need to remove pop up out of drain and first try removing all the hair and immediate stuff that's caught right there. A bottle brush is perfect for cleaning it out. Also try adjusting the pop up to come up higher by raising it in the rod under the sink. That doesn't work let me know but 90% of the time it's a local issue right there.

---------- FOLLOW-UP ----------

QUESTION: No joy.  Cleared the trap thoroughly, had no effect on the behavior.  Still backs up for a minute, then drains quickly till I shut off the water and let the pipes clear.  Which takes a minute.  I can tell because that's how long the banging lasts.  Another strange thing I noticed is that this behavior seems to happen only when I'm running the hot water.  I can run a snake through, but I've snaked a few clogged drains before and never seen any behavior like this.  It's like there's some sort of valve effect happening, where the drain doesn't open fully until some particular amount of water has accumulated.

Did you raise the pop-up?  You didn't say.  I still think that is the issue.  Do this, remove the pop-up completely and then reassemble so water doesn't leak out drain.  Now run water and tell me if it drains normal.  If it does, problem solved.  If it does not, line needs to be snaked from under sink out.  But I am positive it should drain different when you remove the pop-ups.  Pop ups get in the way of the water flow.  They always have.  Water cant drain out if the faucet flow is blocking drain.  Another way to tell is to fill up a pitcher of water and pour it in the drain vs running water in it.  If it drains out great you know also.

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Louie The Plumber


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