All compressors have drain valves at the bottom of the air tanks. These are used both for relieving pressure from the tanks at the end of the day, and to expel the water that builds up due to normal condensation. Allow the compressor to run up to top pressure and shut off automatically. In normal conditions, you may then shut the compressor switch off and open the drain valves. The air pressure that is released will carry excess water out of the tanks. (Note: Open these valves outside; as any rust or oil buildup will be expelled as well, and can cause staining to floors or carpets.) In extreme circumstances, where a lot of water has built up, leave the compressor switch on, so that it will kick on and and continue to pump pressure until the water stops draining. You may then turn the compressor switch off.