REMOVING RUST FROM INSIDE A CONTAINER:

I am trying to remove rust from INSIDE the gas tank on a small engine. Looks like the gel might work but I would appreciate a reply and recommendation. I have removed the tank. If you do have a cleaner, then is there a neutralizer?

...In answer to your question regarding rust removal in your tank:  Cortec suggests using Bullfrog Rust Remover – coat the inside of the tank and leave the solution on as long as necessary.  This product will NOT attack the metal and is biodegradable. Keep the surface from drying during treatment by covering the tank.  

I suggest leaving the tank treated overnight and then simply rinse out with soapy water.  I suggest using some Bullfrog cleaner degreaser in the water for neutralization. Best regards, John Wiermaa, Cortec Corporation

PAINTING METAL:
Can you paint metal after rust blocker has been applied?

The rust blocker should not be painted over.  Restorer can be applied as a primer, and then painted.