<p>While I was getting the wood stained and urethaned today, I had some down time waiting for the various coats to dry. I went through my plumbing plan and figured out exactly what I would need. I had some fitting already, but they weren't the best way to do it. The fittings in the picture are what I plan to use to run the fresh water lines. I will be able to hook-up to a hose for city water input or use a 12v pump to pull water from the fresh water tank. My goal was to make things as simple as possible and be really easy to maintain and replace parts if needed. To that end all water lines will be 1/2 inch flexible hose. </p><p>The city water input hose will attach to the garden hose Y-adapter. One hose will go to the water fill port on the fresh water tank. The other hose will attach to a tee on its way to the kitchen faucet. The water pump will draw water from the fresh water tank and attach to the other port on the same tee on its way to the kitchen faucet. Just before the line from the water input tee attaches to the faucet it will feed into another tee. This will split the water line. One port will go to the cold water side of the faucet. The other port will go to the instant hot water heater and from there return to the hot water side of the faucet. <br><br>I opted to not use any extra check valves in the system. The pump itself has a check valve so water from the city water input can't back-up through it. The two on-off levers on the garden hose Y-adapter will be used to control fresh water input. When no external water hose is attached, both on-off levers will be in the off position. This will keep water from the pump from escaping that way and serve the same function that a check-valve would. It will also keep any water from the tank fill port from escaping from the fill line. <br><br>When I need to fill the water tank, I will attach a water hose to the hose Y-adapter and turn on the valve that leads to the water tank fill port. As soon as the tank is full, turn off the valve. I can keep the hose attached and use it for water with it still attached with the other valve on. <br><br>I think this will be the absolute simplest approach to having both city water hook-up, fresh water tank fill port and 12v pump supplied water in one all-inclusive system using commonly available parts.</p>