[on2wheels52]

I have a general understanding of why an air compressor needs to be drained periodically (and lord knows I've taken enough in hock with what sounds like a quart of water sloshing inside). But why does my portable air tank, even after years of service, not suffer the same malady? The manufacturers of the portables must be aware of this, I've not seen one with a drain.
I had a difficult time with college physics, took me two attempts to pull a hard earned D, so please don't use big words in your explanations.
Jim