This looks like the sort of set up I just was messing with so I will see if I can simplify how I came up with my solution. You have a waterpump and it sucks water from the radiator at the bottom of the pump, pushes it through the engine and the water comes back out of the thermostat housing and back to the radiatior. Only you dont have a radiator so the pump tries to suck water from the bottom hose and pushes water through the engine and tries to push water out of the thermostat housing and then out the exhaust into the lake or pond. Only you also have the jet pump pushing water backwards into the thermostat housing so it is in essence pushing against the water that the water pump is trying to push out of the engine the other way. If you get on the throttle both pumps are trying harder to push water into the same space (thermostathousing) and the only outlets are probably smaller that the volume you are trying to move. That extra pressure of having both pumps trying to fill the same space is probably what is blowing your hose on the water pump housing. If you want to keep the engine water pump you have to put the Jet output into the waterpump at the bottom inlet radiator hose. otherwise the waterpump is working against you. Actually you wouldn't have to put the water into the bottom house, any suction side hose would work but the big one at the bottom would be my first choice. Of course if this doesn't work, my advise is worth exactly what you paid for it.