They do a Mr Muscle two-part foaming pipe clearer -that stuff is fantastic.
We had two sinks, a bath, a dishwasher and a washing machine all coming into the same main waste pipe and they started to all clog up (ten minutes for the bath to drain , washing machine waste backing up etc)... my girlfriend has long hair and it's a rented flat so god-knows when they were installed - at least four years without any maintenance done on them.
Bought this Mr Muscle stuff that has two compartments merging in one bottle, you just pour it out and it foams and goes down the plug hole. I used a third of a bottle on each plughole (bottle recommends one entire bottle) and the stuff must have burnt through whatever was blocking in about 5 minutes. Ever since, no problems at all with the drainage. I have even bought another bottle in case they stop making it but haven't had to use it.
Before this stuff, I had the proper metal-spring cleaning rods for pipes, about ten foot long with a mean looking end to it, and tried EVERYTHING with them to try and clear a path, it made no difference.