Time for us to look for a better plumber

[datgnat]

We've an issue with our kitchen sinks. There are two basins side by side, each with a separate feed that goes into the wall. In the process of troubleshooting why we had a persistent intermittent puddle of water on the shelf below the basins, we discovered plastic fittings that depend merely on friction to be watertight. One piece just slides into another, no taper at all. That's one problem which we have our current plumber to thank for, as he was the one that replaced this (over two visits). However, we noticed the same issue when draining the other basin, which has it's own outlet into the wall, and then demonstrated that when emptying that basin, draining water was backflowing out of the outlet for the first, which would indicate a draining problem in the pipes where they join (in the wall, or the ground). We've noticed no backflow happening when draining other basins, but none of those hold as much water as the kitchen sinks. We need to find a more knowledgeable and thorough plumber, but probably also one with a snake. We've ameliorated the problem with some double-sided tape, but this is something that I imagine will only get worse if unaddressed soon. Anybody have a plumber they are in love with (professionally, at least)?