one thing i do on new (old) boats is put the plug in and fill 'em w/ water, you can see where they're leaking. What i did was dig out ALL the seven layers of silicone, blow it out w/ air wash it and wash it again then use carb cleaner and blow it out again and use the CORRECT silicone adhesive to make a nice clean bead and remove all the excess. After that i found i didnt eveen need a pump....all day