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Question DetailsAsked on 6/6/2017

My double sink in the kitchen and my bathroom sink backed up at the same time. These share a wall back to back.

My double sink in the kitchen, (disposal attached), and my bathroom sink backed up at the same time. My bathroom sink is located directly behind the wall of my kitchen sink. I have no standing water any place else, shower, toilet and laundry are all fine. I currently am trying drain cleaners in both but after 20 min. still no change. Any advice??

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You have a blockage at some point at or downflow of the point where these two lines come together - maybe right at floor level or even a bit above, maybe downstream. There are four possible situations here which I see - see (especially if can see drain line routing in crawlspace or basement) if you can figure out which of the below four cases applies based on where you are having backups, that should help determine the solution.

Though if not a DIY'er and the drain cleaner did not work, then if you think the clog is in the house piping a Plumber or Sewer Cleaning contractor (your Search the List categories to find well-rated and reviewed vendors) would be appropriate. If you think it is in your underground lines, a Sewer Cleaning contractor is more commonly what you want, though some (not all) Plumbers do have sewer routers capable of clearing your entire sewer line to the septic system or street.

1) bathroom sink and kitchen sink are illegally plumbed so the sink drains in upflow of the kitchen trap or vice versa, and the combined trap for both is clogged - causing a backup for both. In that case, cleaning out the trap which both flow through would likely be the solution. If this is the case, you would see, under the kitchen or bathroom sink, a drain line (probably 1-1/2 or 2") coming through the wall from the other sink/basin and connecting in upflow of the gooseneck shaped trap - then another line going out from the trap into the floor or wall from only that one sink/basin - the other one feeding into the blockage trap would be coming into the blockage trap rather than straight down in the wall or floor. If you have only one drain line penetrating the wall or floor below/behind each of the two sinks, leading from the trap but the only other drain pipes come only from the disposal and sink/basin not through the wall, this is NOT the case.

2) bathroom sink and kitchen are wyed into and share a drain line in the wall/floor which is blocked and needs snaking (assuming your drain cleaner did not clear it out). If the bathroom toilet/tub/shower (as applicable) are not backing up this is likely the case, and if no other drains are backing up then the blockage has to be in this shared sink drain line BEFORE it connects to the main drain stack - meaning it is probably within a dozen or less feet of the sinks and can be cleared with the plumbers snake. If you are into DIY, removing the two traps one by one (and cleaning them out while apart) and snaking into the exposed drain line leading into the wall or floor will likely clear the clog - could be from grease and garbage buildup from the kitchen or hair from the bathroom sink. I they were mistakenly wyed together using a true wye instead of using a sanitary wye the blockage is probably at the wye - joining two pipes at a true wye tends to promote blockages.

3) If these are the lowest elevation drains in the house (taking into account other sinks/basins, tubs/showers, toilets and floor drains) AND the sinks are NOT gurgling or backing up when other water is used in the house, then your main stack and underground lines are not backing up and you are in case 2 - a local blockage just in that one branch serving those two sinks/basins. If you ARE getting gurgling or backup when water is run elsewhere, then you have a main stack or underground blockage downstream of where the sink/basin drain line comes into the stack, and a Sewer Cleaner is probably your best bet to rout out the line to the septic tank or street. (Snaking might clear it, but snaking in underground sewer lines generally does not totally clear a blockage, so if the sewer line has not been jetted or routed out in the past 10-20 years [depending on how much hot water is put down the drains (good) and how much grease and disposal garbage is put down the drain (bad)] I would recommend a complete full-diameter routing (my preference - using full-diameter scraper except in deteriorated iron or clay pipe) or jetting during this job - likely only $100 or so more than just breaking up the one clog, which might reform quickly if the general line diameter is reduced by soap scum, fiber, and grease buildup in the lines.

Note - if lowest drains, or lower in elevation than any other water usage and the sink blockage is not draining out over the course of some few minutes (not just a very slow draining out), AND you are NOT getting further backup into it when those other water sources are used, then again the blockage is in case 2) above, NOT in the main stack or sewer lines, because if it was in them and enough of a blockage to prevent drainage from the sink, using those higher elevation sources would cause more backup into the sinks.

4) If these are NOT the lowest elevations drains in the house but there are higher elevation ones in the house, then if the higher elevation drain use does NOT cause additional backup in the sink, you are in case 2) above. If using the upstream sinks/ tub/ shower/ toilet DOES cause backup but lower or same floor usages does not, the blockage is in the stack - the in-house drain piping, and snaking will likely clear it out OK.

Since you say the toilet and shower (assuming you mean in same room or on same floor as the backed up bathroom basin), and laundry are OK - then assuming the backup is not occurring with usages elsewhere in the house, the blockage is in the branch serving the bathroom and the kitchen (case 2) BEFORE it hooks into the stack if there are higher elevation drains, or if kitchen/bath are on top floor, then blockage is in the drain line from kitchen/bath upflow of where the bathroom toilet/shower/laundry drains tie into the main drain stack.

You can also find a number of previous similar backup questions with answers and diagnosis in the Home > Plumbing link under Browse Projects, at lower left.

Answered 3 years ago by LCD

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