Great Idea! chinariderinthesky! I might have to try the Plug with wing nut.....they are called test plugs. I think it might work.
here's what they look like. I could paint it black and drill a small 1/16-1/8 hole thru the top and thru the rubber. it might work. I am unsure of how much air need to be in the tank .... :?:
http://plumbing.hardwarestore.com/52...and-plugs.aspx