Bleed off Air Tanks (water)

First, verify that your coach has an AIR DRYER (or let us know what chassis you have and we can tell you).

If you do, the air tank drains are only a "report card" on the condition of the air dryer. If you ever get anything but clean dry air, the dryer has failed.

Air dryers need to be serviced or replaced with new or reman about every three years in RV service. I STRONGLY recommend only factory parts, new or reman as replacements. When I say factory, I mean the manufacturer of your dryer. There are a lot of cheap overseas replacements. But not sure your air brakes/air suspension is where you want to save a few bucks and HOPE the quality is OK.

So, yes, check it monthly, but if you service the air dryer as you should, you should never have an issue. You should never get water or oil, and worse case (if you don't service the dryer until it fails) is that the desiccant can break down and you will see white powder in the tank drain. Can be a real bear to clean out of the air system.

Saw just this issue on a coach I did a mechanical inspection on two weeks ago.

Probably has a lot to do with where you live, (climate) and how often you use your coach. In California, with monthly use of the coach, I dump mine about 2-3 times a year. I also change out my air dryer filter more often than most....every 2-3 years. I look at filters as cheap insurance and change them more often then recommended.