For a minor blockage, you can try removing visible debris, using a plunger, or cleaning the trap under a sink if you can do so safely. Avoid mixing chemical drain cleaners, as they can damage pipes and cause dangerous splashes, especially if a plumber later needs to work on the drain. Call a licensed plumber if the blockage keeps returning, affects several drains, causes sewage or stormwater to back up, or cannot be cleared with basic methods. A plumber can identify the cause and recommend the safest repair for your particular pipework.