I copied the following directly from the Shaver site, hope it helps:
Hooking up the Hot Water Heater
With an electric hot water heater, we recommend that you remove the pop-up valve and replace it with a 3/4" nipple and a T for your incoming water. Put the pop-up valve back on one side of the T and the circulating pump on the other.
Remove the drain and do the same, putting in a T with the drain on one side and the outgoing water (Pex Pipe) on the other.
Put a surface mount thermostat beside, above or below the bottom element. About $5 - 8 at your local hardware store. Wire it so that 110V goes to one side of the thermostat and the other side is wired to the pump. Common goes straight to the pump, as well as a ground wire.
You just saved $200 for a less efficient side-arm or plate heat exchanger! You can still use the heater as normal. Simply turn the thermostat down lower on the hot water heater than on the thermostat just installed, or turn off your breaker for the pump (or unplug it).
Gas Hot Water Heater
For a gas heater, there is usually a plate than can be removed to gain access to the tank itself. Simply mount the thermostat on the tank and follow the other instructions for water hookup above.
