When I started, I gave it a sloosh out with hot water when I did each nappy wash plus a weekly-ish clean by spraying with eco bathroom cleaner, leaving it to sit then rinsing out with hot water.
Over time though, I got lazy and only gave it a clean if it got dirty or smelly. I always used mesh pail liners anyway and tended to fold nappies in half with the tabs round (but not fastened so they can still come apart in the wash properly) so the bucket rarely had anything dirty touching it. I'd give it a spray and rinse if it was dirty and every couple of months (!) I would leave it filled with water and oxy bleach for an hour then rinse out. I suppose it sounds a bit yuck but I did this for a couple of years with no problems.
