here is one of my livewells. I have since stole a couple of ideas from same and now have the hard wire plug and timer. The only difference between Sam's and mine that I can see is the spray bars are different, oh and mine ALWAYS has bigger fish in it.
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Get the pump at Walmart like Mr. Awesome suggested or go to BPS and there are a few different ones to choose from. If you do not want to take the time to drill a hole on the side of the cooler so the pump can be mounted outside, buy a bilge pump instead of a livewell pump. The bilge can be mounted inside the cooler on the bottom with either small screws with silicone on them or I have used velcro too in the past. 1 pump is plenty. 500 gallons per minute minimum.
Oh and that little screen thing you see on the water intake at the bottom of the cooler...... A MUST HAVE or your pump will clog everytime out with weeds or crayfish parts