i have a 90 gallon fuel tank with old fuel varnish about 1/4 inch thick on the bottom of the tank, do you think 5 gallons on chem dip part# 0905 will cut it? and if yes how long should i allow it to soak? and should i dilute with water?
Berryman Chem-Dip (part #0905) is not suitable for that application. Instead, consider Berryman B-12 Chemtool Fuel System Cleaner (part #0105) to dissolve the varnish. However, if you cannot scrape, blast, or otherwise mechanically remove a significant portion of the varnish first, it will be quite a challenge to clean up and will require multiple applications.