On my sidearms and maybe half a dozen I have installed I plumbed my boiler water through the centre from bottom and out the top straight through the one inch fittings. The 3/4 inch horizontal lower side fitting goes to the bottom tank drain which I replumb to be able to allow a drain if needed. The line should run on a slight up slope to the sidearm. The upper fitting I usually go to the relief hole on the upper side of the tank and move the relief up teed into the tank outlet or a secondary top outlet found on most tanks.. If there are small children in the house I use the side hole to house an aquistat set to 140 degrees F and wire it to run a pump off my primary loop. I just tee in where I want the pump to be and tee in again about 10 inches down stream. In that case I take the top fitting on the sidearm to a tee at the top outlet of the tank. The blueprint for one of the installations called for a check valve just above where I plumbed back in at the top, but I didn't have one so I went without it. Didn't seem to affect the performance at all and the homeowner advised that he was able to turn off the noisy circ pump on his system for the OBW season and still have hot water at his shower and sinks forty feet away. Maybe T have been doing it wrong all thrse years but it has always worked for me....