Filled up the sink . Let it all go in one ; so pump is busy . Ran round , up ladder - watched . Saw 1 drip - couldn’t see exactly where it came from .
As this has been fine for 2 yrs I think it is the pump causing the pipe to vibrate / thud and hence weakening any seal . Could ( once I’ve smeared more tiger seal round the joint ) maybe clamp the white waste pipe to something to restrict any ‘bump’ movement