A Freecycle mod on the other FC thread posted that FC has *no rule* against posting a "wanted" before you post an offer. In some groups, though, it is considered good manners, even if there's no official rule, to post an offer first, or at least to keep some balance between the offers and the wanteds that one posts. My group is no longer an official Freecycle group and has that rule, although I've never seen anyone banned because of it. I don't think anyone's really keeping score except in obvious cases of abuse.
OP, I think your request is perfectly fine. IMO it's not rude to ask for things on Freecycle unless you're doing the gratuitous heartstring-tug thing ("I'm an unemployed, disabled single mom on a fixed income ...") or implying the world owes you a free Whatever. My "wanted" posts generally read like this: "I'm looking for a Whatever. If anyone has a Whatever they're not using, I'd be glad to give it a home." A *little* background or reason for the request is OK ("My Whatever is broken beyond repair." "My doctor recommends I start using a Whatever for my health."), as long as it doesn't get into sob-story territory ("I need a Whatever but I can't affooooord one!")
And I'd offer you *my* kitty litter bucket, except it's where I store used litter between trash days! Can you use a giant popcorn tin with a Christmas light motif instead? No takers for that on my FC group!