Briefly, there should be a tee where the drain valve comes out of the tank with a ball valve on either wing. The long part of the tee runs up to the recirc pump, and there should be a third valve on the line coming into the pump.

The purpose of all this? If you open up a water heater, some water usually flows out and air flows in. After everything is sealed back up and the water pressure is on, that air is going to have to go somewhere. There is a risk that it will run back down the recirc loop, air-lock the pump, and burn it out.

This valving arrangement simplifies flushing. The valve nearest the tank is closed and the other two are opened. Alternatives include loosening the flanges of the pump, but hot water will spray all over the place; or going to the farthest apartment in the recirc loop and opening a tap there. We don't like that because it involves giving notice to tenants and disturbing them.

There are two types of check valves. Swing checks are more common, but spring check valves are better, being less likely to stick open in hard water. For photos of each so you'll know the difference, go to Lingo. What the check valve does is prevent water and sediment from being drawn backward off the bottom of the tank and through the recirc line during periods of heavy use. Cold water from the tank bottom will thrill those unwarily taking showers, while the sediment can clog the pump and piping. We've seen situations where the piping was completely plugged.

The top photo shows a typical recirc return to the bottom of a tank. In both photos, No. 1 is the return destination, No. 2 is the valve that closes to shut it off and force water and air through the recirc, and No. 3 is where the air is flushed out. The third valve, primarily to isolate the pump so it can be easily removed if it fails, isn't shown. The lower photo shows another recirc scheme, where it returns to the cold line upstream from the tank.

One more thing: the nipple that screws into the tank should always be plastic-lined steel, NOT brass. If the latter is used, the anode will react with it and clog the opening with gunk. Then your recirc system will no longer flow and your pump will probably burn out.