Boy, your original post is confusing. Water tank has a fill line, and a vent line, and supply line going to the suction side of the pump. The pump pressurizes the house (boat) water piping, that is hooked up to faucets, spigots, etc. You might have a pulsation dampener tank on the pressure/outlet side of the water pump, but that is a relatively small vessel. My system does not have one. If you water pump is not pressuring the system, the seals
have probably gone out (unless the motor
is not turning, in which case you have burned up the motor). You can typically buy seal sets to replace, or the price
of a water pump is not so high as to be an issue. Just replace it. I carry a spare fresh water pump onboard, and have occasion to need it in the middle of a cruise
. Water tank is low in the boat, and very difficult to access without a pump. Or certainly it is difficult to take a shower
without a pump!