What is blocking my Sink? For the 2nd time my Bathroom sink has become blocked. ...

For the 2nd time my Bathroom sink has become blocked. When we enjoy unblocked it this brown like 'substance' have come up. It has no smell and I suppose it looks similar to the skin you get hold of on custard/hot milk. (I know this sounds daft but we cannot fatom out what is blocking our Sink)
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Answers:    Try pouring boiling hot water down the drain to clear the guk out. Not really sure what is cause this build-up, but when you clear the block, it sounds like it is only just making a ¡§hole¡§ through the guk - and leaving it here to clog up again.

There could also be something stuck in the trap to be precise causing some microbes growth. Try taking out the trap and cleaning it out with bleach up to that time putting it back on.
Fixing a curtain holder to a hole contained...
As others hold mentioned, I'd take the goose collar off and any clean it, or replace it near a new one since you enjoy it out. You could also be picking up blockage material from elsewhere within the system, but I'd say explicitly less feasible.
I would close to to do something completely...