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Question DetailsAsked on 12/26/2017

disposal pushes water down, then it comes back up into the sink

i have taken off the trap at disposal (no blockage), i have removed the dishwasher hose and plugged it (no change). I have run a short snake 3-4 feet long and hit nothing. With the way the water moves down when disposal is on, then comes back when disposal is off, it seems like some kind of air trap elsewhere in the system? how do i find the problem?

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Many disposals have a grinder design, or even an active ejector pump wheel, which pushes or pulls the water through the grinding sieve out of the garbage disposal, so it will actively push the water along the pipe. My guess is there is a blockage somewhere in that line - you should be able to snake from the disposal on through to a foot or two into the wall with that snake to be sure there is no blockage there - commonly is in the horizontal run to the wall from the trap if not in the trap itself, with a buildup of vegetable fiber and grease. Try to remove that to the open end as much as possible, rather than pushing it down into the pipe - I use a stick with a small rag wrapped around it ot reach in at the open top of the pipe, then pull back to the open end dragging and swabbing the gunk out. What is probably happening is the disposal is pushing the water into the pipe till it hits the clog, then up into the connecting drain stack (the pipe manifold running to upper floors and also the vent pipe leading to the roof), so when you turn the disposal off it is running back from that elevated position and back down into the kitchen sink.

If you have other drains at same or lower elevation (tub, shower, toilet, basin, floor drain, etc) and the water is coming out of them, the blockage is DOWNSTREAM of the most downstream drain backing up. Commonly only the lowest elevation one downstream of the sink but upstream of the clog (which might include all drains or maybe only main floor or sometimes only the sink itself) one between the sink and the clog will back up. If no lower drains between sink and the clog, or if the clog is in a branchline only the sink is on, then would back up into the sink only.

I would say a drain pipe cleaning is in order - could be just a snaking in the house with a longer snake would do it, or could need a full-diameter scraping or jetting to the street or septic tank. This full run cleaning is commonly needed every 10-20 years, though in houses dumping a lot of grease down the drain can be as often as every few to 5 years, and some houses with little grease down the drain and goodly hot "soft" water use (especially longish hot showers and full-hot clothes or dishwasher use) can sometimes go 30 years or more before the soap scum and grease buildup so reduces the interior diameter of the pipe that it starts clogging up.

My recommendation if it has to be cleared in the below-ground section - then go ahead and have the pipe routed/jetted all the way to street or septic tank, because just breaking up a clog in that low-slope section of pipe can just cause it to migrate downstream and reclog, causing a new backup in a few hours to days.

One other option - not great if metal drain pipes in the house portion and not good for plastic or cast iron pipes either if done frequently, is using a drain cleaning chemical. I have found, after many brand trials, that the Liquid Plumber Gel works best - sinks to the bottom of the standing water more or less intact rather than diluting in it and many brands do, and sticks to the clog and pipes to attack them better than some which just run right on past anything but complete clogs or get diluted in the standing water. If only a partial clogging, best to let the pipe drain out for awhile (no running of water in house for 15-30 minutes) before using it to minimize dilution in the water standing in the pipes. When using drain cleaners, put down the side of sink (if double sink) without the disposal to minimize risk of damaging the seals in the disposal. If has to go in through disposal dump a couple cups water into the disposal immediately after putting in the drain cleaner to clean out the disposal of the concentrated cleaner - then after job is done flush disposal (and pipes) well with warm soapy water.

Of course Plumbing is the normal Search the List category for in-house snaking - some Plumbers also have full sewer-length cleaning ability, otherwise Sewer Cleaning would be the category to look in for that.

Answered 2 years ago by LCD

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