Originally Posted by harryskater

I cut a big opening in my tank.
I just was not convinced these fluids you can buy to restore the inside of the tank would work, so i took an angle grinder to it, after draining and filling with water. I cut a 300mm square hole, I then got inside with scotch brite and good old elbow grease and cleaned all the grime out and went over it again and again with fresh petrol until i could see my reflection. i also found alot of grime build up in the flow and return in/outlets in the tank. They were completely blocked so i used a small diameter rod, i think stainless welding wire to free it up then went through it with a long pipe cleaner then had a competent welder seal the hole up and check it for leaks.
I think this is the best way to be 100% sure the tank will not give you any more problems.