As someone who repairs air tanks I can tell you it is far cheaper to "blow down" or completely drain your compressor every night after using it than not. In fact if the compressor is not worth $500 it is probably cheaper to replace it. Harbor Freight Tools (and others) also sell an automatic drain kit that cuts into the compressors pressure switch line and replaces the drain valve. As the compressor cycles it bleeds off the water. Hint: put a jug or pan under the drain valve because the water that comes out in humid weather is substancial. Frank