Sploshing for a First-Timer: filling the bathtub

So I'm relatively new to sploshing, but I'm eager to try some of the ideas that I've heard about.
The main thing I want is a way to fill a bathtub with ... something (I don't know what yet). Enough to be able to fully immerse myself in it. As such, I'd need to be able to create a large quantity of thick substance, for relatively cheap (I'm not made of money lol), and have cleanup be relatively easy (i.e. no clogged pipes, stains, or lasting smells). Being edible is a plus, but not a necessity.
Any suggestions?
The main thing I want is a way to fill a bathtub with ... something (I don't know what yet). Enough to be able to fully immerse myself in it. As such, I'd need to be able to create a large quantity of thick substance, for relatively cheap (I'm not made of money lol), and have cleanup be relatively easy (i.e. no clogged pipes, stains, or lasting smells). Being edible is a plus, but not a necessity.
Any suggestions?