Drain gas heater for winter

On the side of the heater, you will see the water connections. Directly underneath them, on that black component that they attach to, there is a drain plug of some description. It may be a draincock, or just a plug. In either case, simply open or remove it to safely drain your heater. In a pinch, you could also disconnect the water connections at those unions (the big grey connectors), but they can be fussy to reassemble, and you run the risk of losing the o-rings.