I haven't done it yet, but I only have easy access to empty detergent buckets, and they aren't very strong. I'm planning to make a cross brace out of small PVC pipe and a cross or X fitting to wedge near the center inside the bucket, hoping that it will provide enough support to keep the sides from collapsing. After reading about your top breaking, perhaps a vertical tube to support the top is in order as well.
Remember, I have not tried this yet ---
So, any advice on how to keep the buckets from collapsing? I am thinking about putting one bucket inside the other for added structural strength. A source for more durable buckets would also be welcomed.
-- OK Don, KD5NRO Norman, OK "The Americans will always do the right thing... after they've exhausted all the alternatives." Sir Winston Churchill '90 300D, '87 300SDL, '81 240D, '78 450SLC, '97 Ply Grand Voyager