fuel tank how much rust is too much rust?

[Fred T]

The POR-15 will take care of pinholes with no problem. Best way to clean out the rust is to put something in the tank and rattle it around. I've used small chains, steel nuts, even 1/2" screen granite. If you have some small rock with sharp edges, it will work. Pour in a handful, slosh it around, then clean out the tank with water. You can then inspect, and see if the tank leaks. No leaks, then order the sealer. Just remember to follow the instructions to the letter.