I just rinse them as they are licked clean. I do have to wash the outsides about once a week though so give the insides a scrub too. Mud, mud, glorious mud.
Hardly ever pony always licks it very clean and it gets used everyday. Sometimes swill a bit of water round on my way down to feed bins. Otherwise it's usually my mum that cleans it, when she was looking after him most of the time it got done everyday as did his water bucket.
If I didn't use it for ages I'd give it a good clean before using again, but he tips most of his food on the floor anyway. Water bucket gets cleaned every few days as don't empty it every day, unless something gets in it or looks dirty. Just top it up.
I have to swill feed buckets everyday as he doesn't lick them clean, ever. And the water bucket has to be scrubbed pretty much everyday as he craps in it pretty much every day, so god dam annoying!
If it wasn't for the above points no I wouldn't do it every day as I couldnt be bothered!