Depends on the animal. For a dog, can be anywhere from fortnightly to monthly depending on how dirty he gets. For a cat, bathing them can result in more injury to the human than the exercise is worth, because a cat cleans himself.
every day or every other day
every day
None! Hamsters groom themselves.
every day
That's untrue. Jews have a custom to bathe on Fridays. At other times, they maintain hygiene the same as everyone else and bathe as needed.
Koalas, like many mammals, bathe by licking themselves.
At least once. You should also wash your hands after and before every meal.
They take care of small animals. They have to clean them, feed them, bathe them, clean the animal's cage or space, and they have to dedicate there time to working with/for the animal.
many
one
The tapir is a relatively hygienic animal, but not obsessively so. A typical Malaysian Lowland tapir, for example, will bathe between once and three times a week, occasionally more frequently in the summer months.
The present tense of "bathe" is "bathing" - still pronounced with a long A as in bathe.