Our kitchen sink has always been slow to drain but has now stopped draining entirely.
The piping dies not go directly outside but we believe snakes around the kitchen (initially behind cupboards and then behind a wall) to the centre of the house where the main waste stack is.
ALL other basins, washing machines, bath, shower, toilets are draining fine.
We got a reputable company to come and rod the pipe, believing there might be a blockage and they really didn't find anything and they left confused, talking about a possible air lock, but saying they would like access to either end of the main straight run of the pipe to be able to put down a bigger rod. Needless to say we are not keen to take out the (new) kitchen units and part of the wall to expose the end of the pipe nearest the sink.
We have found an inspection cover in the utility room, by the main stack, but the building work has not made lifting this easy as they have tiled over the top of it.
We have tried trickling water down the pipe, just beyond the U-bend under the sink, but it backed up very quickly (under 0.5 litre of water put down) but when we look at the pipe (i.e. remove this water) it looks empty.

Any advice on what our next step should be without dismantling the house!) would be really appreciated.

Hi Sandra,
Did your plumber remove the :J" bend of the trap,( see image ) and snake the lateral drain in the wall? Or does your drain go into the floor and not in the wall? Let me know. Tom

Yes he removed the J bend and put the rod through from there.
The pipe definitely goes along the inside of the wall on which the sink is mounted, we could see it before the kitchen was re-done and then disappears into wall at the end, we assume at that point it does a right hand 90 degree turn to run behind that wall, we just can't see it. The otherside of that wall (though not a party wall) is the neighbours property.

My next question is, did the plumber go on the roof and snake the kitchen roof vent. That's the line that would cause air lock when draining if it were blocked. That's the line he should have snaked next if he didn't catch it in the wall. Regards, Tom

No he didn't, should that be the next course of action before we do anything else?

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they left confused, talking about a possible air lock

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Once the magic phase "air lock" came up the next logical place to snake was the kitchen roof vent. Your plumber was either too lazy to go up on the roof of else he didn't have the experience enough to realize that he should have. In any respect you should call him back to finish the job he started. Good luck, Tom

Just thought I'd update on the final outcome on this issue.

The Kitchen didn't have a separate vent, so that wasn't the issue.

We managed to free the inspection cover (hours of chiseling out the grout - neighbours very understanding :o ) and got a different man in who pressure washed the pipe and got the blockage out. Years of build-up removed has resulted in a sink that drains better than it has ever done before :D

Thanks for the advice though.

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The Kitchen didn't have a separate vent,

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is that what the plumber told you. Sandra, Every fixture that has a trap, must, by law, have a vent. If you don't have a vent then you have a illegal "S" trap. Glad the plumber got you fixed up. Regards, Tom