You have to admit that we are a good team, Patricia and me. Our drain problem was not getting better. I am in UK. Patricia is holding the fort.
Thinks. M. Michael the plumber. Last time he came he was REALLY efficient and not expensive. So I found his number and emailed it to Pat.
Pat phoned him. "I'll be right there !"
It turns out that it is what I thought it was in the first place - a build up of undissolved washing powder.
He's coming with his tube washer and he says once he's done that all will be OK once more.
Bravo M Michael.