There are times when it isn't always possible to remove blockages from the sink end. If the waste pipe discharges into a gully, try pushing a garden hose into the pipe from outside. You might also have to turn on the tap to get the obstruction cleared.

When a plunger fails to clear a blockage, try using a plumber's snake otherwise known as spiral cleaner. You should find them in many hardware stores. You will have to first disconnect the pipe from the trap, and then push the wire into the pipe. Turn the handle of the spiral, when the spiral makes contact with the obstruction blocking the pipe. The obstruction will usually shift after this is done.

Taking the bottle trap apart is an option when you are unable to clear a blocked waste pipe from either end. Before dismantling the trap, remember to put a bucket underneath, and to plug the sink's plug-hole. After the obstruction is removed, rinse out the trap before reassembling.