Tank Slosh
Sense you have had fuel in the tank I highly advise against using any kind of slosh sealent. The safe way is to remove the tanks, drill them apart, clean off all of the old seal and proseal with a scotch brite type rotoloc pad and a die grinder. Re seal the tank with new proseal, as soon as your done attach it to the wing to let it cure in it's place. Make sure you clean the bare aluminum with MEK (really clean it good! not just wipe it down) and scratch the alclad anywhere your going to put the proseal. Always use gloves and never touch the bare aluminum with your bare hand. My first RV-4 had slosh in the tank and it started floating around like cooked egg white, and I did the above fix, and yes I had to paint it again.
RT