kitchen drain problem [resolved]

[mitxi.drain]

we're in a tiny 3rd story apartement building
possibly one toilet and roof vent above us and many toilets and drains below us
see crappy drawing if you want a laugh

kitchen sink has drained slowly since we moved in a year ago
sometimes just slowly (2 minutes) and other times, it takes over 2 hours (this is truely completely random as far as we can tell)
it backs up into our washer too if I have it connected
I'm fairly convinced this is not a clog and it can't be the main vent either since 2 other drains to that main have never had any problems
(please see drawing)

things we've tried:
-plunger (never seems to make any difference
-pipe snake (5 meters) - always came out "clean" and never got stuck on anything other than the pipe bends
-more than a dozen different drain cleaner liquids and gels
-taking apart as many of the pieces of pipe towards the main drain as possible
-I'm planning to get a cheap USB endoscope but I'm not sure it is long enough to be useful

 

[Reach4]

kitchen sink has drained slowly since we moved in a year ago
sometimes just slowly (2 minutes) and other times, it takes over 2 hours (this is truely completely random as far as we can tell)

When the kitchen sink has not been used overnight or longer, how much water does it take to see water backing up in the sink. One way to determine this is to collect water in one or more 5-gallon buckets, and pour. Another way is to figure out how many gpm your kitchen faucet puts out on full cold, and time how much time it takes for the sink to start backing up.

I'm fairly convinced this is not a clog and it can't be the main vent either since 2 other drains to that main have never had any problems

It is very probably a clog. I can't think of a different explanation. It's not a vent problem.

(please see drawing)

I tried. What is "H2O heater" in that drawing? Do you mean a floor drain at the water heater? Water heaters do not hook up to drain lines.

That toilet appears to flow up. I know that cannot happen.

 

[Sponsor]

 

[mitxi.drain]

When the kitchen sink has not been used overnight or longer, how much water does it take to see water backing up in the sink. One way to determine this is to collect water in one or more 5-gallon buckets, and pour. Another way is to figure out how many gpm your kitchen faucet puts out on full cold, and time how much time it takes for the sink to start backing up.

It is very probably a clog. I can't think of a different explanation. It's not a vent problem.

I tried. What is "H2O heater" in that drawing? Do you mean a floor drain at the water heater? Water heaters do not hook up to drain lines.

That toilet appears to flow up. I know that cannot happen.

Thanks for the interest.

I will try to get a more precise answer for you but we have to wait for it to drain or disassemble the trap and make a mess.
First, as previously stated, it varies a lot. Sometimes a couple liters will drain in a few minutes. However, as I type this, and seemingly more and more often, 1 liter is taking over an hour to drain. If we run water into the sink with tap full open, it backs up within seconds. If the tap is a quarter open, it can drain indefinitely.

H2O = water; yes, the water heater (hangs on the wet wall in the water column) has an overflow drain (I presume) which is connected to the same drain pipe

Sorry the drawing sucks:
-it is missing the part that goes down from the toilet (the sewer main for the building splits into two going all of the way down the building) I guess I forgot it because I think it is so far removed from being relevant
-the pipe gradients/slope/falls are not depicted properly at all (but they all seem to descend at least 1cm per meter of travel which I'm told is acceptable)

Cheers

 

[Reach4]

I will try to get a more precise answer for you but we have to wait for it to drain or disassemble the trap and make a mess.
First, as previously stated, it varies a lot.

Waiting 8 hours is probably enough for the test.

Let me tell you what the number would mean... pipes have a volume. The blockage that I think is there has a hole or two in it, but that limits the flow. If the water is added quickly enough, that leakage could be either compensated for or ignored. In the US, the trap would usually be about 1.5 inches and the drain pipe 1.5 or 2 inches.

Anyway , from the volume of water, and the presumed size of the drain pipes, we could compute an approximate distance in the path from the sink drain, through the trap, through the drain pipes, to the clog.

Your snake may have pushed an 8 mm hole through the clog. The clog may have been resiliant enough to partially close back up after the snake has been pulled, or the 8 mm hole stayed and allowed some water to pass slowly.

Kitchen clogs often happen where the pipe after the trap and sanitary tee go from vertical down to horizontal. I circled what I think that is in the picture I marked up.

 

[mitxi.drain]

Waiting 8 hours is probably enough for the test.

Let me tell you what the number would mean... pipes have a volume. The blockage that I think is there has a hole or two in it, but that limits the flow. If the water is added quickly enough, that leakage could be either compensated for or ignored. In the US, the trap would usually be about 1.5 inches and the drain pipe 1.5 or 2 inches.

Anyway , from the volume of water, and the presumed size of the drain pipes, we could compute an approximate distance in the path from the sink drain, through the trap, through the drain pipes, to the clog.

Your snake may have pushed an 8 mm hole through the clog. The clog may have been resiliant enough to partially close back up after the snake has been pulled, or the 8 mm hole stayed and allowed some water to pass slowly.

Kitchen clogs often happen where the pipe after the trap and sanitary tee go from vertical down to horizontal. I circled what I think that is in the picture I marked up.

OK, so things are draining well now.
Everybody can say "I told you so", because it must have been a clog almost right where Reach4 said.
We managed to get it unclogged by purposely blocking every hole (overflow, washer, and H2O heater) in the circuit and going to town with a plunger and sink full of very hot water until our arms were tired. Perhaps it was clear grease and/or perhaps it was a piece of plastic bag or...? I guess we'll never know...
Thanks to everybody for the help and encouragement!