Home DIY

Hmmm, I'd already removed the u-bend before posting. When I replaced it just now I had to twist the waste unit and grey seal a little to align, this has immediately stopped the leak (for now at least), tested via emptying baby bath through it. Keeping an eye on it / pan beneath it still for now though. Ta.

If you can move the lower part its not tight enough hence the leak. You probably tightened it a little when you moved it but it should be tightened properly.