57. Should any bhikkhu bathe at intervals of less than half a month, except at the proper occasions, it is to be confessed. Here the proper occasions are these: the last month and a half of the hot season, the first month of the rains, these two and a half months being a time of heat, a time of fever; (also) a time of illness; a time of work; a time of going on a journey; a time of wind or rain. These are the proper occasions here.
Patimokkha, chapter VIII:6
Bathing. Although Pc 57 forbids a bhikkhu from bathing at intervals of less than half a month, we noted in the discussion of that rule that it was apparently intended as a temporary disciplinary measure for bhikkhus who had inconvenienced King Bimbisāra when he wanted to bathe in the hot spring near Rājagaha. When the Buddha later added exemptions to the rule, he so relaxed it that he virtually rescinded it. In addition, Mv.V.13 explicitly rescinds the rule in all parts of the world outside of the central Ganges Valley.
In the time of the Buddha, bathing was done in a river, a bathing tank, a sauna, or a showering place. Instead of soap, people used an unscented powder called chunam, which was kneaded with water into a dough-like paste. Bhikkhus are explicitly allowed to use powdered dung, clay, or dye-dregs; according to the Commentary, ordinary chunam would come under "dye-dregs." A bhikkhu with an itching rash, a small boil, or a running sore, or whose body smells bad (in the words of the Commentary, "with a body odor like that of a horse") may use scented fragrant powders. At present, the Great Standards would allow soap under the allowance for clay, and scented soaps or deodorants under the allowance for scented powders for a bhikkhu with a strong body odor. Otherwise, the use of scents is listed among the bad habits prohibited by Cv.V.36 (see Chapter 10).
The etiquette when bathing in a group is that a junior bhikkhu should not bathe in front of an elder bhikkhu or, if bathing in a river, upstream from him. If one is able and willing (and, of course, if the elder bhikkhus are amenable), one may look after the needs of elder bhikkhus while they are bathing. An example of this, given in the Commentary, is scrubbing them. When scrubbing another or oneself, one may use one's hand or a rope or pad of cloth. Sponges, which apparently were not known in the time of the Buddha, would probably be included under pad of cloth.
One is not allowed to rub one's body with a wooden hand, a string of red powder beads — according to the Commentary, this means bathing powder mixed with powdered stone (cinnabar?) and formed into beads — or with a scrubber incised with a "dragon-teeth" pattern. A bhikkhu who is ill, however, may use an unincised scrubber. In the time of the Buddha, young men while bathing would rub their bodies against trees, against walls, against one another (this was called a "fully immersed massage"), or against rubbing posts (aṭṭhāna, which according to the Commentary, took their name from their being incised with a pattern like a chess board (aṭṭhapada)) in order to toughen their muscles. Bhikkhus are explicitly forbidden from rubbing their bodies in any of these ways. However, they are allowed to massage themselves and one another with their hands.
In another context — cleaning one's feet before entering a dwelling — one is allowed to step on foot wipers made of stone, stone fragments, and pumice ("sea-foam stone"), so it would seem reasonable that the use of pumice or other stones to scrub off stubborn dirt while bathing would also be permitted.
When leaving the water after bathing, one should make way for those entering the water.
One is allowed to dry oneself with a water wiper — which the non-offense clauses for Pc 86 say may be made of ivory, horn, or wood — or with a piece of cloth.
Source: Access to Insight.