You have to buy a kiddie pool from the Sporting Goods store in JT Ult, then go back to your dorm room and put on swimwear. Then when you go to stream on Niche it should give you the option to do a hot tub stream.
When I wrote this comment the kiddie pool was in the sporting goods store, but it's been moved since then! It should be in the toy store in JT Ult now.
