What is usually worn in private hot tubs?
Generally speaking I’d ask before going to the party what kind of swimwear is expected, if any. Most private hot tub parties I’ve gone to pretty much everybody, myself included went nude. Same goes with swim parties if the pool area is private. Base it though too on your comfort level. If you’re ok with being nude in a social setting, go for it. If not, wear what makes you comfortable, even if you’re the only one clothed. I’m a nudist so it’s no big deal for me to go nude in mixed company. If swimwear is expected, I wear my speedos and I always make sure to take my own towel.