I can probably help, if I knew what you're attempting to do. I've built livewells and bait tanks out of everything from buckets, to barrels, to coolers, to old truck toolboxes.
on my jon, my gravity live well has a threaded drain, or fill however you look at it. I have a pump with removable base (snaps together and a part very easy) screw base in drain hole. I use that to file the live well quickly and to circulate the water. Have spry nozzle on top. I also have a circulate pump I use after I pull the main pump and store it.
The only pain is before I exit the water I have to pull the pump and insert the plug. Not a big deal though.
oh, forgot to mention I do have a portable bilge pump that I can use to fill or drain the live well if I choose not to mess with the drain plug and fill pump.