If you are thinking about future return lines, for either a SDS or EFii system, you'll need a duplex valve. MUCH easier to plumb all of that now during the building processs than to retrofit later. Well at least the bulkhead fittings for the tunnel and side skins. The actual hoses (or rigid tubes if you are so inclined) can be added later. Definitely install the tank return port in the rib NOW--before the tanks are sealed up. You can order your Andair duplex valve and extension and install it now--just cap off the return ports in the valve. We have a specific way to configure the valve if you are thinking about using our package.