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Question DetailsAsked on 12/18/2016

Installed a new garbage disposal, did leak test and other sink filled up with water. How do I fix this?

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3 Answers


Hope you did not change out the disposal unnecessarily.

Assuming you have the normal plumbing - trace the piping to check, answer below if fairly normal piping. You can also google a search phrase like this - images of kitchen sink trap - for more common (and some uncommon) plumbing arrangements and how-to-clean-a-trap articles.

Normal plumbing would be garbage disposal on one side sink of a double sink (usually right side), that drain pipe or "tailpiece" leads from disposal into the drain pipe ("tailpiece") coming down from the other sink, connecting just above the gooseneck or P-trap below the other sink - then the combined flows go through the trap and exit stubout or "waste pipe" after that (usually into the wall, sometimes down through floor), like in the following image - second photograph in the article. Though sometimes the garbage disposal tailpiece leads directly into to the trap and the other sink comes into its tailpiece from the side like is shown in the first sketch in the link - actually a better way to plub it but commonly there is not enough headroom under there to do that right because of the height of the disposal. Images here -

Anyway, both sink sides lead into the trap, which is U-shaped to hold water so sewer gases can't come up through the sinks). The trap is the U-shaped pipe hanging down then leading back up and out to the drain line stubout or "tailpiece" to the wall (or occasionally down into the floor). If the other sink filled with water during the test (and the garbage disposal probably filled up too or the right sink drained slowly, even if you did not see it down in the disposal) then the trap or the waste stubout (or possibly but a lot less likely the drainline somewhere downflow from there) is plugged, at least partly. Could be that was your initial problem - or rarely in the process of connecting the pipes up food debris or a clog works free in the disposal tailpiece and moves down to the trap and clogs it up.

Look at the sketches and second photo in link above - if you have plastic pipe with threaded connections like in the photo, it is easy to take the trap out and clean it (keep track of the nylon bevel washers at each "nut" and which way they face as you take it apart - may stay on pipe or come off with the nut and then can fall out).

In some cases like in this following link (second and fifth photos in article) the trap is plumbed so you can remove everything (U or P trap and the elbow coming out of it at the end) all the way to the straight waste pipe, allowing you to clean it out too. In others (6th and 7th photos in first link below and the second link also) the waste pipe stubout from the wall may have a rigid elbow waste pipe or a glued joint at the elbow leading into it or the joint is hidden in the wall, so it is harder to get through the elbow and into the waste pipe stubout - though for a few bucks you can buy a 2 foot flexible plastic hair remover which you can slide in there in at least partly remove the gunk.

The trap is easy to clean out with a twisted paper towel - or just shoving a paper towel through it. The waste pipe sometimes a hair remover will pull clumps of food (kitchen) or hair (bathrooms) - take it a few inches at a time, pulling the hair removal tool all the way out each time, because if you shove it all the way in and hook a massive clog it can get wedged in the pipe - then you are in trouble with the clog and the tool in there. Ditto with paper towel or rag - twist it into the pipe a few inches at a time (hence paper towels easier because you can dispose of after each partial pass), working a bit deeper each time. Do NOT just shove it in there all the way - that can pack the accumulated grundge into one massive clog that only a plumbers snake will remove.

NOTE - the grundge in the trap can sometimes slowly eat through plastic bags, so dispose of the removed material and paper towels in outside trash can or dumpster as soon as the job is done - don't leave in kitchen or bathroom trashcan.

NOTE - the trap is always full of water (and grundge), so when you loosen the connections and remove it you will dump a cup or two of water out, so do it over a bucket or pan. And both the trap and waste pipe will be full of really nasty soap scum, hair or food debris, etc - not anyway near bad as going into a sewer line but not especially pleasant if you are squeemish.

If you have soldered copper or brass piping, old rusted galvanized pipe, cast iron, or glued-joint plastic pipe, unless a serious DIY'er you probably need a plumber. And while he is there I would have him install (if feasible and relatively easy, which it usually is unless piping is over about 50-60 years old) a threaded removeable trap with compression fittings so next time you can remove and clean it yourself - commonly a every 10-20 year job.


Some pros here will scream at me if I say this, but you could, assuming the water gradually drops down over time, use Liquid Plumber Gel (the gel type works WAYYYYY better than other cleaners because it adheres to the clog material to let it eat away at it) in the sink that backed up. Wait till the water level has dropped away, then carefully pour in per instructions, keeping it from contact with the sink itself - especially if not stainless or porcelain. May have to pour it in incrementally every minute or two to avoid backing up into the sink. Then finish out clearing per instructions on bottle. Unless it is a pretty complete clog of eggshells or nutshells (which should not be in there in the first place) it will normally clear it out. I would NOT recommend using this if you have copper or bronze pipe, or pretty old corroded steel or cast iron pipe because it can corrode them. Also I would not use it in any type of natural stone sink because of the risk of eating away at it or etching/staining it.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services


I forgot to say WHY many pros would scream at me mentioning using drain cleaner - some because it takes work away from them of course, but also because it is very bad for septic systems (kills the bacteria that make the system work, so promotes leach field clogging and excessive solids buildup in the tank if used often), and is bad for the pipes - especially metal ones, but also bad for the thin PVC or PE pipes commonly used under sinks, and can eat away at gaskets and any rubber sleeve repairs or joints in the system - and these are more common with modern pipes than old ones. In fact, many modern buried sewer pipes have gasketed connections at each joint rather than glued or welded or threaded, so you can get leaks from frequent or prolonged drain cleaner use.

Also, never put drain cleaner through the garbage disposal.

Answered 3 years ago by LCD

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