A sento is a public bath. It is not an onsen resort. Customs are a little different.
Some things are written on the wall - wash with soap before you get into the communal bath. Don’t drip water on the changing room floor, or put your towel into the tub. But there are unwritten rules that a bandai or local elder used to tell you. For example, it is rude to sit on the edge of the tub. If you tried that in the sento down the hill the bandai would stick his or her head into the bathing area and shout to you to, “get down please.”
Another hint, if there here are two baths in the men’s side and two in the woman’s. One bath is kept very hot, the other you can add old water to if you need to cool it. You should find out which is which before you start adding water.
A cover I painted for Sento Magazine