Occasionally discharge pipes and drains get blocked due to various causes such as newspaper or kitchen towels being flushed, fatty build ups and other none flush-able items being put down the W/C. The challenge for the plumber or homeowner / responsible person is to unblock the pipe with the least disruption. Unblocking methods can vary for different circumstances utilising drain rods, plungers and in some cases chemicals.
Drain rods are passed down the pipe and screwed together in sections until the blockage is met then giving a couple (or three) of hits the obstruction is dislodged and then hopefully with the build up of pressure behind it will be washed away.
An alternative method is to use a drain auger or spring. These are passed down the pipe and rotated dislodging the blockage. The most common method of unblocking a drain (drain cleaning) could quite possibly be the most effective and this is the plunger method. The reason this gets great results is because it creates pressure on the obstruction of at minimum 101.3kN/m2 which is atmospheric pressure. So as the plunger is removed it leave behind a void which forms a partial vacuum. When plunging your sink wastes, make sure the over flow is suitably blocked as well otherwise air will travel down it and relieve the negative pressure in the pipe.
Some chemicals are also good for unblocking drains, most commonly used on bath and shower wastes due to a build up of hair, dead skin cells and fatty deposits from soap (soap scum). I’ve had the best results with Caustic soda, other chemicals are available usually branded. Just make sure you read the label before use or handling if you fancy having a go yourself. Or just let your qualified plumber do the hard work for you.