Yup, it's always drained when we are done playing with it. I got a piece of ply wood to put over the top as a cover. I still rinse it every time to get all the gunk off before I fill it again.
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I use a shower curtain liner as a cover. It's not perfect, but it works pretty well. We empty and refill the table about twice a week depending on the weather.
Re: For those of you who have a water table without a cover