I am building a new boat and this one will have an integral bait tank and cooler. I took a 4 gallon bucket and cut it in 2 and spliced it 12" wider. This keeps the tank low and retains the round corners. Also allows just a bit more volume than any regular bucket.
The keel on this boat is 2 layers of 2" Dow pink stuff foam. That puts just about everything above the water line. To avoid having the pump sit low where it could get shorted out I came up with a scheme to get it primed and this also allows me a hose for washing things out. A necessity since the bait tank and cooler are integral.
So today I tested my theory as to how to prime my bait tank pump. Turn the bait tank inflow valve off. Turn the hose outflow valve on. Turn the pump on. Suck on the outflow hose. The pump will prime and water will immediately fill the outflow hose. Turn the tank inflow on. Turn the outflow hose valve off. Bait tank will fill in about a minute.