Forget the Permatex or any other sealant all that's needed is plenty of Teflon tape on threaded end of thread/barb tank fittings...nothing except a little dishwashing liquid to lubricate hose connections. Inspection ports, including tank level indicators, should be secured with screws and rubber gaskets (easy to make....rubber gasket material is readily available from any hardware store), NO sealant. Replace o-rings on caps.
--Peggie