I have a few square 2, 3, and 5 gallon buckets, they originally contained some type of equine feeding supplement. Believe me i washed the heck out of em! Unfortunately I've had em a while and the stickers are so worn off i can't remember what the name of the product was, but if anyone in your area keeps horses they are likely to have a few of those buckets lying around. A lot of Equine supplements come in square buckets. Just an idea for getting em cheap instead of buying specifically made fish buckets at your LFS.
If anyone really thinks there is a chance of residue in these buckets even after washing them a lot please do let me know. I don't use them often, but if there's even a chance they are unsafe I won't be using them anymore.
No matter how much I learn or know I'm still gonna be a NOOB, but that doesn't mean I'm an idiot!