I think it'd be very hard to really clean anything with a plug for drainage. Those darn ducks (and geese) make SUCH a poopy mess. Even two days of swimming with a couple ducks and there's a layer of poop sludge in the bottom of their pool. That's why I like kiddy pools, they're light, easy to dump out and wash out on a regular basis. Plus, as someone who has to buy stock tanks for actual stock, those pools are a HECK of a lot less expensive. LOL! You can buy a nice big one for $15 at the big box store, plenty of room for several ducks at a time and it'll last for years even through the abuse of being flipped over to dump it out every other day all spring, summer and fall. Plus: no ramps needed; they can jump/fly in and out without help.
I've found the waterfowl don't much care about the depth of their water; it's the surface area they like. Big enough to zoom around in, get your friends in with you. To get the same surface area in a stock tank you're looking at upwards of $200. Even if you replaced your kiddy pool yearly you'd be looking at a decade to get your money back out of the stock tank and with it buried it probably wouldn't last that long anyway.
ETA: I've had the same big, $15 kiddy pool for the ducks and geese now for 3 years and it's still going strong. And that included one summer of it being abused by pigs, to boot.
