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Question DetailsAsked on 5/11/2017

I live in a 3rd floor apartment; 2nd floor neighbor's kitchen sink overflowed last night. Could I be at fault?

My neighbor was out of town and had someone look at their apartment yesterday and said the kitchen sink flooded. My kitchen is right above. I have not had any problems draining water; furthermore, the sink was barely used two days prior to the incident and only once several hours prior to the reports of flooding. I'm almost positive the first-floor apartment isn't having any issues. What could be causing the overflow? Moreover, if there is a blockage, wouldn't it be between the 2nd and 1st floor? Could food or debris from my sink have descended down and caused a blockage? I'm usually careful about removing food, but I admit that some could have escaped through.

Also, we had a great deal of rain last night (the same night the issue was reported); could rain have flowed through the vent pipe from the roof and overflowed the kitchen sink?

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3 Answers


EXTREMELY unlikely the vent pipe caused it even if you had literally FEET of monsoon rains - would require it be plugged pretty thoroughly and improperly plumbed both, so that is pretty much out as a cause.

Depending on how the pipes run, it is possible that debris from your (or other 2nd floor or higher apartments) could have caused a blockage that resulted in the backup. However, unlesss you are putting stuff down the drains or toilet which should not be, it would not be your "fault" - it would be the result of otehr tenant putting improper stuff down the drains/toilet or a plumbing issue like old pipes which have not been routed out every 5-10 years or so (for apartment buildings, commonly more like 10-20 years for single-family residences). Since an apartment, this sounds like an issue for building maintenance to handle - and should be handled ASAP because if there is a partial blockage in the drain lines, that sink backup is likely to happen again when upstairs people flush or empty a tub or otherwise use large amounts of water - usually backups from a partial blockage are first noticed when a clothes washer is emptying because that is usually the highest flow volume discharge in a residence. Actually, I wonder if the apartment watcher checked all drains - I would have expected any floor drain or shower or tub to have been the first thing to overflow, but it is possible the kitchens in an apartment stack are on a different drainline than the bathrooms. If the sink backed up, unless the dishwasher drain line is properly elevated through an air gap above sink rim level, it is also likely there was flooding under the sink and backup into the dishwasher.

Since the backup occurred without the sink being used and on the second floor, sounds like a blockage in the "stack" - the network of pipes connecting the various apartments, because if the blockage was in-ground the backup would have occurred in basement (if any) or else in first-floor apartments, so should have been noticed assuming they are occupied. Of course, the building super should check all areas visually (common areas, basement, unoccupied apartments, etc) or by asking tenants (for the apartments) to see just which areas were affected. Yes, as you say - if the basement / first floor apartments did not get any flooding, the blockage would be above the first floor connections or low down on the second floor on the stack branch serving that apartment which did flood.

Answered 3 years ago by LCD


Thanks for the answer LCD! I just find it a bit unlikely that food could float down from my drain and not cause any drainage issues for my sink and instead block up my neighbors; does this seem unlikely to anyone else or am I just trying to absolve myself? Like I said I have been guilty of letting some food slip by on occassion. The day of the incident I also did a great number of dishes, but it was several hours before anyone became aware of the issue. I don't know anything about plumbing but I believe that their kitchen is directly below mine and the bathrooms for both units are on the other side of the apartment. Does anyone know if this could affect how the "stacks" are arranged? Thanks for any further help!

Answered 3 years ago by Spike89


Could be the kitchens are on one branch or stack, and the bathroom another - like this diagram where toilets and other fixtures are on separate lines until you get to the underground portion -

However, what you put down it should not be a problem unless you (or some other apartment on same line) dump a lot of grease or really fibrous garbage down the sink, because the following shows what the connection of their sink line to the line dropping from your floor should look like -

You can see from the photos of the pieces of pipe that the connection has a curved entry to ensure the flow is aligned with the direction of flow in the pipe it is connecting to - so unless it was improperly plumbed with a straight Tee connection (whcih can cause backups at the connection point), the only way a backup can reasonably occur is if there is a damaged pipe, or a blockage in the stack which then backs up into the lowest elevationn drain connecting in above the blockage point.

Again - building management should be checking for other points of overflow in the building so it can be cleaned up before it goes all moldy, and the lines should be snaked or better yet jetted or routed to clear out the blockage.

Answered 3 years ago by LCD

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