If its above the pool water height it'll drain back into the pool to the top pip by opening the air release valve. Then you can take the top half off and some water can stay in the bottom.
The hula hoop gasket may need lube or replacing. Clean the groove it sits in on both halves if you're in there.
Before you go that far, try tightening the clamps. I've never bottomed mine out and can always get a couple more turns by hitting clamps either side of the knob. A rubber mallot would be nice but I always just use the bottom of my fists and it hurts a little. Lol. If they wobble at all when you hit the outside edges, the knob will easily turn a couple more times. Again, I've never found my end, I give up after several rounds after it was originally hand tight.