when you say pump, do you mean impeller ? if so the housing that goes over the impeller should be completely flush i think there maybe a gasket, not sure now. anyway theres a spout on the top of the housing that fits into a rubber/plastic piece, then theres i pipe that goes into it above which takes the water to powerhead, if this isn't connected right water would escape and your be pumping water internally. im only going from passed experience ive had to take the gearbox off again to sort it out
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