If you flush the cooling system with a water pump attached use the old water pump and not the new one to prevent impurities from contaminating the new pump. Dont put it on too thick just enough to hold the gasket in place on the block or on the pump.

Best Gasket 7014 1937 48 Flathead Ford V8 Water Pump Gaskets
Installing water pump gasket. Do not force the pump on by striking the pump shaft. Position the new pump straight onto the mounting surface of the engine block. If youre installing a conventional gasket use a gasket sealant theyre available in sprays liquids and tubes with specialized formulas for a variety of applications. The water pump gasket is a simple sheet comprised of gasket paper rubber silicone metal felt and fiberglass or plastic polymer. It fills the gap between the engine and the water pump in your vehicle. Make sure the bolt holes align.
Install the new water pump. Put an even bead of sealant along the edge of the part but dont use too much sealant. Use the gasket and put the gasket maker on either side of it. An improper seating damaged seal or misaligned gasket can mean the water pump is not operating efficiently or worse is under undue stress from misalignment. Double check that all the bolts are in place and in their. It will do the same job and work just as well.
Carefully follow installation instructions. Dont apply sealant to an o ring or a dry seal. Only apply sealant if specifically recommended by the vehicle manufacturer. When changing a water pump replace all old gaskets and seals with new ones. Should leave you in good stead. If youre a full time auto repair pro or dedicated diyer gasket makers and flange sealants are products youll want to keep on hand to save time and money.
Without the gasket the coolant flowing between the water pump and the engine block would undoubtedly leak out. Old gaskets and seals should be replaced by new ones. Then apply a dab of rtv sealant to the bolts and install the bolts finger tight to hold your new water pump in place.