[Guy]

Our Newell is very similar to your water bay. One  12 volt water pump, and no 120 volt water pumps. Newell used a water manifold before there were water manifolds, by using a hydraulic/ pnuematic manifold of the day .Time for the way back machine. I believe that your  manifold is factory, as it looks just like mine. It was a solid piece of solid  billet  aluminum, with two 2 3/4 npt holes going all the way through the billet,   four bolt holes through the billet but not the water jacket to mount to a floor or wall or bracket. It has  3/4 npt threads on either end to enable the manifold maker to machine the interior of the manifold. Included are a  handfull of 1/2 npt inlet/outlets. 1 outlet  is used to feed a large single step  water filter that in turn feeds cold water to the kitchen sink, bath valve, toilet, water heater, restroom sink.  A 2nd 1/2 npt goes to a two step filter which provides water to the ice maker, and a special tap on the sink for filtered drinking water. A 3rd 1/2 npt is used for hookup of city water. A 4th 1/2 npt  receives pressurized water from the water pump.These 4  1/2 npt inlet/outlets all have  ball valves at the manifold.

The final inlet outlet is 3/4 npt, although with our simple coaches 1/2 npt would be fine. This outlet has a 3 way ball valve and controls water going to the bottom of the water storage tank and the water pump. It allows the filling of the water storage tank, or sending water from the storage tank to the 12 volt water pump, for times when we are not hooked up to city water. This valve needs to have the city water valve open to fill the water storage tank , closed to provide water via the water pump.

We have an added valve to send water to  the black water tank for rinsing , along with an anti back flow valve.

It is very easy to leave the existing copper pipe in your coach, and use pex fittings to adapt to a new manifold. I could not find a simple manifold, and ordered a manifold from McMaster Car  like our 38 year old one, which fits on our existing verticle fiberglass mounting bracket . Pex is your friend. Good luck