I'm sorry for the inconvenience. The plumbing was indeed very unfortunate. It happens when too many long hairs get in the bathroom sink (for instance by combing hair above the sink). It's also unfortunate I was on holiday, so I couldn't fix it myself. That's why I asked if I should ask a friend to do it for me instead.
It's also easily fixed by emptying a bottle of a special liquid in the bathroom sink, as I indicated in a detailed message with clear instructions. You wait 15 minutes (just checked the bottle; sorry I wrote 2 hours) and the problem is gone, because it dissolves the hairs that got stuck in the bathroom sink. The liquid was in a cupboard, as pointed out to you (left lowest shelf, orange bottle). This simple meassure or accepting the help of a friend of mine would have made your stay more comfortable.