I have a 4hp 12 gallon air compressor in the garage. Been there being used for no doubt 10 years plus. I needed to take it down to the farm for some work and when I pulled it out, it must have at least 1/3 of the tank filled with water. It is heavy too. I know water tanks and such have a "ballast system". But I'm not sure about air compressors. The tank does a clean out valve at the bottom. Should it be emptied? Does all the water come out? Thank you.