Try to acquire buckets from restaurants rather than construction sites, as they are far less likely to have been exposed to a lot of sunlight/UV radiation. Sitting on a partly-full sun-rotted bucket and having it fall apart under you is not something you need under survival conditions (and it would make a big mess on your bathroom carpet).

ki4buc: thinking a little more on your question, I would STRONGLY suggest that you invest in some sawdust, as-is or in pellet form. You may not believe how much it will absorb odor and keep down flies. Otherwise, the alternative would be to fill and close a bunch of small bags and put them into a large bag, and all those bags mean that it would all have to go to the landfill rather than a sewage treatment facility because no one is going to want to empty all those little bags. And if you just let the waste accumulate without bagging or covering it, you're going to have an awful stinky, fly-ridden, maggotty mess.

And if you want to 'invest' in a pickup load of sawdust (not PT), it doesn't have to be stored dry. Just dump it in a corner of your yard or under a tree and let it sit until you need it. If it advances into a state of compost, no problem, you still use it as-is.

Sue