PropDoc
Why the hurry to get a bottom pour pot? From what I've read I'm happy staying with my Coleman stove and pot, pouring with a ladel. I can pour my six cavity 44-40 MAV Dutchman mold with one Lyman ladel without refilling it. That's all the pour I need at one time. I make my rifle bullets one at a time, and it's plenty big for that.
I am not an expert by any means, but it makes sense to me that once in the mix, tin does not float to the top. In fact, once my lead is clean, I get almost no junk to the top of my steel pot, and quite a bit to the top of my cast iron pot. I've concluded, after emptying the iron pot and finding rust on the bottom, that what I'm scraping off the top is iron oxide.
If you are not casting much I don't see the need to go to the bottom pour unless you need to do your casting indoors and want the cleanliness (?) that may come with casting that way. I do it out on the porch and don't worry much.
Wayne