At night we let it mellow, not only for the water, but because the bathroom is right next to DD's room and the loo wakes her up sometimes. We used to do it during the day as well, but since moving into our new place we flush each time because the toilet is a water saver one and has hardly any water in it, so it kind of needs it done. We clean with white vinegar and bicarb every day or two. I always check to make sure there aren't any skids, either from me or emptying DD's nappy (something we've only started probably 2 weeks ago) and just give it a quick brush if there's any evidence lol.