Before you take a hot bath, please check the following;
1. Please take off your underwear before you go into the bathing area.
2. Please wash yourself thoroughly before getting into the bathtub.
(Please sit down while taking a shower, and do not waste water.)
3. Please keep your towel out of the bathtub.
4. Please do not run in the bathing area, and do not swim in the bathtub.
5. Please refrain from washing your clothes or underwear.
6. Please wipe yourself off before going into the dressing area.
Please do not take a hot bath just before or after the meal, and also when you get drunk.
How to take bath in Japan (PDF)