It is a compressed air gun for stuff like this. I pump it up, make sure the seal is good around the drain hole, make sure the overflow is covered and fire it.
It sends a shockwave through the drain and no blockage can resist the shockwave (not yet anyway).
The gun isn't very big so it can be manovered into awkward places. It is really good and works on toilets as well.
Just one thing to remember...it is very, very, very, very messy though if you forget to stop up any overflows or cover the toilet rim - take it from me - you only forget this bit of advice once
_
Unblocking a drain
