The lady at the shop said I had enough to make a bath-full of lube, but not to do that because if you got into the bath you'd never get out.

Empirical evidence shows that's not true. And it only takes a third of a 10oz bottle. It's not all that thick at that sort of dilution, but still slippery. It's best to crawl out of the tub.

I find myself wondering if a hot-tub pump could deal with it. It'd have to be a one-night sort of affair, because you wouldn't want to chlorinate it...