If you are planning on taking a trip to Japan, it is important to know that, unlike in the West, the toilet and the bathtub belong to separate rooms in a Japanese home, and each has its own set of rules for proper behavior and usage.
Bathing Etiquette:
In Japan, the sole purpose of the bathtub is to soak away the troubles of the day, not to clean your body. All members of a household share the same bathwater, so actual washing of your birthday suit is done outside the tub, before getting in.
There are generally two areas to every bathroom: the first contains a sink and an area to undress; the second contains the actual bathtub, as well as an adjacent shower for washing yourself clean.
Japanese bathtubs tend to be shorter, but also much deeper, than their Western counterparts. Because bathing is such an important part of the daily unwind, most homes are equipped with tubs that can either be programmed or set to heat to a specific, desired temperature. In Japan, this desired temperature usually means a temperature that is much hotter than what people from the United States are used to or find comfortable. It may take some time to adjust.
Seniority generally determines which member of the household gets to bathe first, and this usually means that the father enjoys the first soak. Whenever a guest is present, however, first rights is given to the visitor. The water in the tub is not drained until the last member of the family has finished his bath, and, even then, sometimes the water is saved to be used to fill the washing machine. When the bath is filled but not in use, a lid is placed on top to keep heat, as well as evaporating water, from escaping.
In some older or rural homes that do not have a bathtub, a visit to a sento, or public bathhouse, is still common.
For information on using a traditional Japanese-style toilet, be sure to read Japanese Bathroom Etiquette - The Toilet.

