Bill’s comments relate a common enough issue and is worth checking into.
But also, Mark, is your “Fresh Water Dump” rocker switch off (pressed downward and held on “Closed” for a few seconds), and if so do you see or hear water spilling on the ground under the edge of the coach anywhere? If the switch is off (it may need to be held off for some seconds) but you have water spilling underneath the rig, it is a common malady to have a jammed or otherwise faulty water tank dump valve, letting water out as fast as it’s going in.
Forgive me if you already know all of the following, but I’ll proffer it just in case you don’t: With the pump switch off, the top right blue “Tank Fill” valve on your Manabloc manifold should be turned using the red “key” handle so its black center is horizontally oriented to fill the tank, and straight up and down for direct city water pressure to the coach. This presumes your ‘05 Marquis’ water bay is similar enough to our ‘06 Monterey in basic concepts.
Joel