Proper way to bypass heater?

Heywodja said
You could always cut the nipple and tread a plug into it, this way you never have to worry about that cheap *** nipple failing, ask me how I know.

No need. The nipple bases are already pipe thread.

So just remove the nipples and thread in the proper size pipe plugs available at any good hardware store.

(Brass plugs for less possible rust)