you can get 5 gallon PE buckets used for paint with a snap on lid. They will hold diesel just fine and don't leak or spill. Around $3 a piece. Finding some place to dispose of it might be an issue.

If you have new tanks made, FWIW, here is what I insisted upon: weld them from the inside, at least on the 8 seams before you get to the top. That leaves a clean weld bead inside rather than an open crack or an ugly "sugar" of oxidized aluminum. Make sure the bottom slopes towards a corner. In that corner have them put a small sump, doesn't need to be very deep, just a couple of inches, maybe 6 inches square. This is where all the water and debris will end up. Directly above that, put an access port, can be just a 1 1/4 inch NPTF plug. Then in the future, you can stick a tube down there from an oil change suction type pump and remove the bad stuff. The suction tube for the pickup should end just above this sump. Make sure there is a large (like 12" diam) cleanout port in the top, one for each baffled section if necessary.

Most tanks are welded from the outside because it is easier. That leaves a crack at the seam (if the penetration is incomplete) or at the very least the oxidized aluminum "sugar" that is the result of the back side not being protected by the Argon gas. These features trap water droplets and dirt, and seem to be the place where corrosion and bacteria start. Many tanks don't have a well defined low point, so contaminants slosh around over a wide area on the bottom.