I too used to use a bathroom to hang negs. to dry. Then a number of years ago I bought a Durst UT100 film drying unit which I dismantle and pack away after use, (even though I have a converted darkroom).(posted 8115 days ago)Actually the bathroom is perhaps the worst room in a house for dust. OK, it doesn't see as much use as a living room or a kitchen but the use it does see is all dust generating. Body hair, skin particles are all deposited frrely and scattered about by vigorous rubbing with towels which also provides their own source of fibres.
If you also happen to have a lavatory in the same room then the use of modern soft toilet tissue is a splendid source of dust. Just stand in a beam of sunlight with a toilet roll held so that you can view it against a dark background then tear along the perforations and you'll see magnificent clouds of dust being freed.
Naturally all of this dust settles around the room, when you go in it all gets stirred up and lands again - some of it on your negs, and of course not merely landing there but 'glueing' itself into the soft emulsion!
Trevor Littlewood.