2000 yamah 50HP no water out pissing after impellrr change

i just finished this and I am getting a lot of water coming out the area where the shift arm comes out of the lower unit and nothing out of the top end. i took it back apart and put the muffs on the lower unit. there is a lot of water escaping from the top of the waterpump housing, where the driveshaft runs through it. there is flow through the water outlet on top of the pump housing as well. it looks like there should be some sort of seal on top of the pump housing, like the alpha units. but the housing is all hard plastic. there is a gap between the impeller cup and the top of the housing but nothing goes there, i looked at the parts breakout andit doesnt show anything.
i sent compressed air up through the water intake tube of the upper unit and i hear air coming through the combustion chamber but there seems to be alot of back pressure when i let go of the trigger. this is a river boat.

Yeah, there should be a rubber seal and a cap that slides in the water outlet hole. Maybe those got stuck to the upper casing or they fell out and you didn't notice. The water pump repair kit should have them, but if you only bought the impeller, you should be able to buy just the seal and the cap. If yamahaonlineparts.com doesn't show them on one of the diagrams, I'd be very surprised.

^^^Agreed. Or when reinstalling LU the mid section water tube did not seat into housing.