Provide him with a dust bath, not a water bath, anonymous. In the wild, lycanroc (and rockruff, for that matter) roll around in volcanic ash in order to clean themselves, and this can be simulated in domestic settings, either by spreading commercially sold pokémon dust in a manmade sand pit or by simply leaving a bare patch of dirt in your lawn, depending on whether or not you live in a dust-heavy environment. Either way, be sure to clean your lycanroc’s bathing area regularly by raking the used dust away and replacing it with new dust every few days.
It’s also highly recommended that you follow up your lycanroc’s dust bath with a thorough brushing to remove excess dust.
This may seem like it’s not enough, but really, a thorough dust bath clears oils and dirt off the fur, scrubs the skin beneath clean, and knocks off and suffocates parasites. It will actually be perfectly sufficient unless your lycanroc is too weak to bathe himself or too caked in dirt for a dust bath to be effective. In these cases, you may need to use a water bath as well, but be sure to keep your lycanroc’s rock collar as dry as possible. Moreover, it’s imperative to follow up with a dust bath anyway, either by allowing your lycanroc to administer one himself or by helping your lycanroc to roll in his dust pit. This will help draw out any moisture from his fur and allow his body to dry.