Shelby & Seymour get baths once a week and "1/2 baths" in between. I recently purchased some dry bath shampoo at the groomers. So far it seems to be helping, so those "in-betweens" may be becoming fewer.
(Being a girl, with long hair, it seems like Miss Shelby needs to be cleaned more due to her "squatting" when she goes pee..)