My partner had a similar problem, his would'nt hold water, kept kicking the bilge pump on, he fould some loose screws, that hold the lip down, on top of his live well, he re-tightened them, and used some lock-tight, it pretty much solved the problem. However, if yous is slow to fill, and is not holding water, it sould like it may be in the fill and drain hoses.
Filling it up with a water hose, put some food coloring in the water, look for leaks in 5-10 mins.... Tr