[mike31154]

I've been using a Rubbermaid roughneck like the one pictured (lid is hinged) for a number of years as my water change mixing container. Holds about 22 gals of water safely. It's strong, but does bow out from the weight of the water. Since it's on the basement floor I finally clued in that a piece of styrofoam underneath the container would allow the water to heat up more efficiently. It's full of water with powerheads running & heaters on anywhere from a few days to more than a week before water changes. You should be fine.

Used a similar (forgot the brand, no name I guess) container for a while. It was a bit thinner & the bottom cracked eventually.