an easy fix for that is to build a wood frame around them to prevent bowing, but its not exactly pretty. i use a 30g tub for my w/d and i can fill it all the way to the top, and yeah it does bow, but it wonk break.
I have a 300 gal Rubbermaid that I use as a fish pond… I can fill it until it overflows with no bowing concerns… Rubbermaid makes a 150 & 100 gal version that is built just as tough…
I have a cheap clear plastic Rubbermaid ‘storage’ tub that holds about 28 gal… I filled it to 25 gal and it bowed like crazy… but didn’t break or leak…