Have a blocked drain been like it for a few months, only serves bathroom sinks so just 'grey' water , can't think whats blocking it [not even a dribble gets thru]. From Manhole right next to outlet cannot get rods to it as not flexible enough. Any suggestions, ? tried pressure washer down it and cleared it with small boat pump but just grey water. Tried a couple of bottles of 'one shot' but no effect.