Shouldn't the middle junction be above the waterline?

We made the mistake of putting bottle traps in some of our sinks. Dreadful things.

I call it a junction but it is just were two pipes are coupled together. This coupling is beneath the level at which the water rises up to empty back out. I watched a guy explain how susceptible the junction is to leaking but he didn't suggest teflon tape which I ended up using to end my sink trap leak.

I want an engineers explanation for the gasket less junction.

The bottle trap looks like it could clog very easily.

Tape will fix the leak, but might result in water backing up into the sink.

Well, that was already a problem that is occurring from a place far beyond the P trap. I doubt the tape will be much of a problem any time soon.

Why isn't this middle junction designed with a gasket? — Nils Loc

It should not need a gasket if installed properly. The seal is caused by the difference in the angles of the 2 sections, male and female. The principle is the same as the combustion engine's intake and exhaust valves.
There is a small difference in the angles so that when the two part meet with in a limited amount of degrees the tightening of the locking nut pushes them together and forms a contact point around the whole circumference.

Problems usually occur when the angle of contact is incorrect due to faulty alignment. That is why the are made in several sections, to give enough flexibility. Most people think that a leak means that the locking nut is not tight enough and proceed to over tighten it and warp the union.

Plumbing 101.

Thanks Sir,

But I'm still sort of bewildered by the design choice. It'd be so much easier on those installing a p trap if they didn't have to perfectly align that particular junction. Tightening the other couplings can throw off good alignment. I spent too much time messing with it even after knowing I had to align it.

It must be about manufacturing complexity (extra cost) for that particular union.

There is still a mystery about this I'm afraid will never be uncovered.

It'll be great content for Netflix's next season of Unsolved Mysteries.

It'll be great content for Netflix's next season of Unsolved Mysteries. — Nils Loc

There is a simple solution, buy a flexible hose like those used for washing machines and install it so that the U-bend is about the same shape as the gas trap tube. It works just as well and you only have to worry about the 2 ends.

It works just as well and you only have to worry about the 2 ends. — Sir2u

It's ok. I'm throwing my sink out and will wash my dishes in the local creek from now on.

:rofl: :cool: