I'll put my opinion in as well. I used the sterilite tubs and like others say, they do not hold up very long. I use the mortar mixing tubs with great success, but if you use them with short pots (like 4" pots) they're so deep that your plants get flooded. I use perlite in my mix, and that all floats out and I have to repot. I drilled a drainage hole about halfway up the side of the tub so it won't flood. If i need to leave for an extended period of time, say up to a week, I put wine corks in the holes so the tray will hold more water for while I'm gone and I move the smaller pots to more shallow pans like a cat litter box or something similar.
I also agree that the mortar mixing tubs make excellent bog gardens! Dwayne and I use them to grow irises, water hyacinths, lotuses, and grow out trays for small water lillies. They're excellent for growing U. gibba as well. U. gibba grows well anywhere, but in my experience it doesn't bloom well if it is floating. If it's affixed to some time of soil in shallow water, it blooms continuously. Our mortar tray of gibba is usually covered in yellow blooms during the summer.
Will