[Richard]

Here is a quick and high payback project for you. Remove the petcocks from those drain tanks and replace with DOT fittings. Run the DOT nylon air hose to a convenient location. Terminate the lines with stainless quarter turn valves. Run an exit line from the valve to under the coach frame.

Now you can stand on the ground, and drain each tank while watching what comes out.

Well that is, unless you enjoy a rust water and oil shower a couple of times a year.