My current hot water tank, presumably installed by a DIY former homeowner, has severe corrosion on the inlet tube and must be replaced due to a considerable leak.

Were I to DIY, how could I prevent this from happening again? Is several wraps of Teflon tape the usual method of installation, or should I use some kind of pipe dope? What will last the life of the tank or beyond?

On the new tank I imagine I'll use flexible hose on the inlet, which will have an O-ring. Will that be sufficient?

The outlet is in good shape and there's a pink wrap on the threads.

Severely corroded hot water tank inlet Hot water tank inlet and outlet

1 Answer 1


You need to use dielectric unions between the copper pipes and steel water heater. They prevent electric current from flowing through the metal, which prevents galvanic corrosion.

  • Would a flexible hose be sufficient? (Can flexible hoses be used on the hot output?) I just watched a video on dielectric unions - it was mentioned that tanks now have the union built in vis a vis the plastic inserts in the inlet and outlet - would I still need a separate thread-on union?
    – Matt
    May 26, 2019 at 12:29
  • 1
    @Matt - I wouldn't use a flexible hose. I haven't heard about built-in dielectric unions - if that's the case, and your new water heater has them, you should be okay. Otherwise just get a set and put them in. They're cheap, readily available, and work well. For some reason, the phrase "dielectric union" is frequently used, but usually they're not actually unions. They're actually dielectric nipples - short sections of pipe.
    – Mark
    May 26, 2019 at 15:23

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