Under sink plumbing - help! (or... have I got a ghost?!)

[Maxf]

I've had a leak under my kitchen sink - the u-bend joint (plastic screw in joint) is very loose and leaking. This happened a month ago and I replaced the seals and tightened it up, but it has come finger loose again!

What on earth could be causing the kitchen u-bend to be loosening itself?

Stupidly I didn't take a photo this morning, but all I can think is that it's because it is connected to the dishwasher somehow. The dishwasher drain pipe connects to the waste pipe under the sink, but after the u-bend. Last night the dishwasher wouldn't drain (I suspect it's being loaded with very dirty plates and the filter needs cleaning), and the u-bend came loose.

Anybody got any ideas what could be happening? Could the hot dishwasher water be making the pipe come unscrewed? Could some kind of air pressure/vacuum be causing the problem. with the dishwasher not draining?

A proper plumber fitted it all 2 years ago.

[pim]

Start with the dishwasher first.Clean the filter and the small rubber pipe connecting to the u bend under the sink.

We have a dishwasher similar set up as yours.I never put plates in covered in food.Rinse them before putting in the dishwasher.

[2lefthands]

First leak likely perished seal. You have potentially then overtightened on replacing seal, hot water causes pipework and joints to expand slightly, it jumps a thread and abracadabra, plumbing ghost myth debunked.

Get it all the time, if a joint leaks, replace don't fix, it's a £3 kit.

[Maxf]

Thank you both!