Need simple diagram

It sounds as if you have a 12 vdc rv type pump, this would have a pressure switch built in so that when you open the faucet it senses a loss of pressure and runs, when the faucet is closed it senses a build up of pressure and kicks off. if you have no water going to it it should run constant when you supply 12 volts. Do not hook it to 110 vac, you will be buying a new pump.

Just put it by the fresh water tank, hook the supply line and run your supply line as normal, 1 line to your cold side and 1 line to your demand heater and then out of that to your hot side.

You may want to consider adding a hose bib to your supply side so if you are where water is available you just hook a hose and not run the pump.

My suggestion is to go online to camping world and look at the plumbing section, it will give you an idea of what you need. I suggest using flexible pex pipe, available at lowes etc, it stands up well to vibration when on the road. Rigid PVC tends to crack with vibration.

Not a plumber but a long time rv'er so I have done my share of plumbing repairs. Also you could stop at an rv sale lot and look under the cabinets, a lot of the plumbing is exposed and you can get ideas seeing how they do it.

I also am not a plumber...and I didn't even sleep at a Holiday Inn Express last night...however, I also am an RV'er and I recently replumbed my trailer-mounted smoker. The attached diagram is how I did my smoker (do not try to infer dimensions or anything like that...it's meant to be a working schematic). It only shows the supply side. It sounds like you have a handle on the drains, but if you have any specific questions, just ask.

A few points:
- I agree with thunderalley about flexible pipe. The PEX is somewhat flexible. I ended up using CPVC, but transitioned to SS flex hoses on either side of the pump so that the pump vibrations don't transfer to your entire trailer. Also, my understanding is that you can use PEX or CPVC for all lines, hot and cold, but PVC should not be used for hot.
- I set mine up to be easily winterized. That includes a kit that goes at the inlet of the pump (allows you to bypass the freshwater tank and pull antifreeze directly from the bottle) and a bypass kit for the water heater, which you probably won't need if you are using an on-demand heater. Those two kits allow me to just drain the freshwater tank and water heater tank and not have to fill them with the antifreeze.
- I have a 2 basin SS sink and a separate handwash sink, so I tee'd off the hot and cold lines to feed each (just get adapters to go from whatever lines you're using to the sink flex hose fittings).
- On the hot supply, I tee'd off an additional line and adapted it to a 25 ft retractable air hose reel (from Harbor Freight). I adapted the other end of the hose reel to a water hose fitting a put a spray nozzle on it. The hose reel is mounted inside the cabinet that holds all my plumbing, with the hose running through a large grommet. I can grab that nozzle, pull out the hose, and get to any part of my 5x12 ft trailer to wash it down, etc. And since it's straight off the water heater, it's very hot.
- My water heater is an Atwood 6 gallon, gas and electric, with electronic ignition. If I plug my smoker in to 120 VAC, I can run the water heater on both gas and electric. If I don't have power, I can still run it on gas only. I have a 12V deep cycle marine battery that will run the electronic ignition system. That's probably a lot different than your on-demand setup, so I won't get into wiring details...but if you have questions, ask.

What you probably have is a converter, rather than an inverter (though it could be both). I put a converter on mine. If I'm plugged into 120 VAC, the converter will run all the 12V loads, AND keep the battery charged. When the smoker is sitting next to my house, I normally keep it plugged in, just like I do my RV. That ensures the battery is always topped off. A converter/inverter will also convert back to 120 VAC, so you can run normal AC loads off your 12V battery. That's how many RVs work. Since everything on my smoker is 12V (including some LED floodlights I added), I didn't see the need to spend more on an inverter. I am also normally plugged in anywhere I'm cooking, and if I don't have power, I can use a small generator.

I hope this helps...let me know if you have any other specific questions.

Here is a picture of my smoker. It doesn't show the plumbing details, which are all inside the diamond plate aluminum cabinet, but it does show the white city/gravity water hatch (below the handwash sink). It also shows where I plug in my electrical cord, which is a small round black surface mount plug on the side, just above the fender. You can also see my grey water tank drain under the trailer, below the sinks.