Put a hand packed with drywall screws into your tank and shake them about vigorously for various minutes. These will dislodge any unfastened particles of rust. In the situation of Fiberglass and plastic tanks, this will tough up the tank inside, improving upon adhesion. There are some different sections on https://caswellengineering68899.ziblogs.com/37809535/the-2-minute-rule-for-caswell-engineering