Don't do it. You'll spend a lot of money, and it will still leak, and possibly break. I had made a table top fountain out of a pot I sealed with black gunk made for that specific job - leaked and totally ruined my NEW hand-installed (by me) hardwood floor.
I got RubberMaid type tubs at local resale stores, up to 50 gallons, and only $3-$5 a piece. Just be sure there are no holes, which can be hard to see, and be sure the plastic is sturdy. One of mine bulged so far it was really misshapen, and I was afraid it wouldn't hold up. Some others I have squished in a flower bed inbetween the house and a concrete retaining wall, so they're supported on the sides.