Why not a bead of silicone caulkig down the inside and a few turns of self amalgamating tape around the outside to hold it together?

I would hate to see these tanks trashed.

I have two 4x5 ones now and I am searching patiently for more 4x5 ones with the floating lids at the right price to do a dev/stop/fix sequenece, and be able to adapt with a spare or more to do a line of e-6.