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Zeigh 06-20-2012 12:15 PM

Secondary Drain (Relief Drain) Clogged

What is the correct terminology for the secondary drain (relief drain at the top of the basin) in a bathroom sink?

Now, any suggestions for unclogging this in a Kohler sink? I am replacing the faucett in a sink and just discovered that the entire area for this secondary drain is clogged with some kind of dry crusty substance, almost like rust. In checking another sink just like it, I found that filling the basin with water all the way to such a drain port shows that it is also clogged. As long as nobody ever, ever leaves the water running in a closed sink, I guess that this won't be a problem. HA, but you don't know my family. If there is an easy fix while I have easy access to the drain, I might as well take care of the matter.

Any suggestions?

Hating plumbing because I accidently bump my head too often,
Dr. Z.

AllanJ 06-20-2012 12:40 PM

I think it is called "the overflow."

I suggest disassembling the drain pipe from the bottom of the basin and finding the channel that leads up to the opening at the top of the basin.

Carefully use a coat hanger or similar stiff wire to scrape the channel clean on the inside, but do not force the wire in or around bends.

I would also suggest running muriatic acid down the channel (and catching it and running it through several times) except you need to keep that from splashing around or spilling on the floor or inside the vanity. Also not getting it on the surface of the basin or on metal or Formica or marble surfaces.

Zeigh 06-20-2012 01:02 PM


Since I posted my question, I have indeed unclogged the overflow drain. it appears to be just a super heavy buildup of rust. I can chip away allot of it, but as you guessed, there is some that is virtually impossible to get to physically.

I would like to avoid the muriatic acid suggestion. No matter how careful I am, past hazmat experience has taught me that I will spill some of it and ruin the finish of the surroundings. Is there a chemical that eats away rust and is more user friendly? Even a very slow acting one? One that is safe for the cheap plastic drain that i am about to install? Now that the overflow sink channel is clear, all I am really doing is just general maintenance for the future.

Dr. Z.

Alan 06-20-2012 09:49 PM

Is your sink a porcelain coated steel or a cast iron?

Zeigh 06-20-2012 09:57 PM

I am going to guess iron, but can check tomorrow if it is crucial...

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