If there are litter boxes in the shower in the bathroom then they’re ready to be cleaned. Please scrape as much cat litter out and into the trash as you can to minimize what goes down the drain. There is a special smiley face scrubbing sponge that works well. You can use Simple Green or dish soap for the first scrub. Rinse well and leave upside down in the shower area to dry. Once dry you can wipe down with a Clorox/Lysol wipe and let dry.