Bud mentioned a Thread Chase Nipple. I've been able to file chip release "slots" into pipe nipples or pipe plugs and use them to clean threads. With a Pipe Thread TAP, it's possible to go too deep and end up oversized. You could to this: Take the new anode to a plumbing department and determine the pipe thread size. Then get a nipple several inches long and cut the slots into it. Drill a hole crosswise in the other end to slide a T-Handle into. That way you can keep it straight and steady. Hard enough to get the anode threaded into a Suburban, so make a tool with some reach.