To prevent flooding, many bathtub and sinks have an overflow pipe or tube. The overflow pipe runs from drain holes near the top of the basin down to the main drain pipe. If the water level should rise too close to the top of the basin, the water drains away through the overflow. Not as prone to clogging as the main drain, you may need to unblock a water overflow pipe should the tube become clogged with hair, mould or fungus.
Place the tip of flexible funnel in the drain hole at the top of the basin. If the drain hole is covered with a guard plate remove the plate with a screwdriver.
Pour drain cleaner into the funnel, following the manufacturer's instructions. Liquid foaming drain cleaner is manufactured in a two-part solution that is activated when the solution mixes together as it is poured into the drain. Allow the drain cleaner to sit in the drain according to the manufacturer's instructions.
Fill the basin with water to reach the level of the overflow pipe's drain hole. Repeat the procedure if the overflow tube is not draining freely.
Insert a small drain snake or long-handled wire brush into the top of the overflow tube. Work the snake or brush all the way to the bottom of the tube and back up again while twisting the handle in a circular motion.