A plumber warns about the costly mistake of pouring oil or fat down the sink, which can lead to blockages. He demonstrated how to clean out the pipes effectively. Tips for avoiding sink blockages include pouring hot water down the drain or using a vinegar and baking soda mixture. Properly dispose of cooking oil by letting it cool, transferring it to a sealable container, and then either freezing it or taking it to a recycling centre. Don’t let oil and fat cause serious damage to your drainage system.