The hot tubs that are sexual are sexual not because of the presence of an hot tub but because of the actions (and the clothers) of the people in it...as long as you define those 2 things with strict rules you can have both bannable hot tubs and not bannable hot tubs without causing confusion.

Give me an example of a strict ruleset.

Describe the line, where everything on one side is fine, and everything on the other side is not. Where 'regular' hot-tubbing in a bikini is fine and non-sexual and you'd be okay with a child doing it on your platform, and the exact pinpoint where it becomes a sexual stream and it isn't okay for anyone to do.