Sink drains are designed to carry water, and water only. And like all blockages, there is not a single possible cause.
Common blockages to wash trough is often caused by a build up of clothing material, like lint, caught in the piping.
Tree roots require an entry point into the drain. Ground movement and/or, roots putting pressure on the pipe until it cracks, or a pipe joint which was not sealed completely upon installation is very common. A cracked connection from the waste pipe to the large drain pipe is often a point where tree roots enter the drain, or tree roots can blocked the main drainage pipe outside, not allowing the water to empty from the sink. The only permanent remedy is to seal the roots entry point. In some cases will require a section of the pipe to be replaced.
Warning In older properties which still have the original galvanized steel waste pipes, the pipe is corroding on the inside of the pipe. As the rust expands inside the pipe, the inside pipe diameter becomes much smaller and the rough rusty surface allows for material flowing down the sink to become caught. These older pipes can be a continual source of problems. Never use a caustic soda or drain-o products on properties with metal drains. It will speed up the rusting process, leading to more blockages and the need to replace them much sooner due to the pipe rusting through completely.
For assistance with your plumbing blockages, please call 0414935499