J: On many water heaters there are two tappings to accomodate [email protected] reief valves. The unused opening is plugged with a 3/4″ plug that is provided by the manufaturer.
Take another look at the heater in question, and see if there isn’t in fact an 1-1/8″ hex nut
barely protruding through the sheet metal jacket. It may even be obscured somewhat by the foamed insulation that is used in most new heaters.
If none is found, there are retrofit anodes available that can be inserted in the hot water
Without an anode to protect the inside of that tank, it’s useful life will be greatly reduced.