Lye, also called caustic soda and sodium hydroxide, is a substance frequently used to make soap. Lye is available in liquid, pellet, flake or powder from most home improvement or hardware stores. It is an effective substance for use in unclogging drains and is often one of the active ingredients in commercially available drain cleaners. Lye works because it is caustic and actually dissolves hair and grease, which are the root causes of the drain clog.
Put on gloves, eye protection and a mask before opening the lye. Lye is extremely caustic and will burn your skin.
Place 2 to 3 tsp. of lye directly into the hole of the clogged drain.
Turn on the faucet for one to two seconds to dispense enough water to wet the lye. Only 1 or 2 tbsp. of water is required, so do not allow the faucet to run for more than a few seconds.
Open any nearby windows, or turn on the ventilation fan. Leave the room, and close the door to the room to contain the fumes.
Allow the lye solution to sit for 10 to 15 minutes. Run clean, hot water through the pipes for one to two minutes to rinse all traces of the lye out of the pipes.