Installed a 2.5g water heater expansion tank off of a existing 3/4 brass T on copper cold supply line on wall next to tank. Brass T does not point straight up but away from wall about 22 degrees. Used Teflon tape, 5-6 wraps everywhere on brass fittings, except at base of tank where manufacturer requires pipe dope also. Tank is vertical with threaded stub at bottom. (Sorry I can't do pix here). Tank is supported with metal strapping both horizontally and vertically.

From crooked T and cold line hanging on wall: small nipple, 90d elbow, small nipple, another second elbow pointing upward and tank.

Got a pinhole leak at bottom of first elbow. Each time I undo straps and retighten, this joint swings down due to the angle of the threads and the weight of the tank.That creates a space for water to invade, despite my tightening it.

I'm wondering if I should just get rid of this T, replace with a shark bite pointing outward, and repair using shark bites? Each redo requires a complete disassembly as parts can't be rotated due to the wall...and one threaded piece un- does the first elbow a bit.

Will the T plus 2 pipe dope that I smeared on the pinhole leak work to seal and harden? Not looking for new idea/ways to plumb. Already bought the shark bites but I'd prefer to get the brass fittings tight.

Is there a trick to get a threaded fitting to point in a certain direction when you are finished screwing?

  • Pipe dope will not harden the leak needs to be properly sealed. Do not over tighten the fitting if things are correct when snug and pointing the correct direction stop. Armstrong method works great for straight couplings but not 45’s and 90’s. You might be able to use shark bite on the cold side but not at the tank ? There is a required separation I don’t remember if it is 16,18 or 24”.
    – Ed Beal
    Jun 23 at 23:06
  • Thread the thing on there first and then do the sweat fitting. Usually it's a valve, so you sweat a nipple while it's on a bench so you can cool it asap and so you don't melt its innards while you do field work, and also so this doesn't happen.
    – Mazura
    Jun 24 at 1:45

If after several tries you can't get the joint between short nipple and first elbow to seal, inspect them carefully for damage and consider replacing them.

Temporarily install a cap or plug in place of the expansion tank -- that'll allow you to turn on the water, check for leaks, and perhaps tighten leaky joints further without full disassembly. Remove the cap/plug and install the expansion tank when all the other joints have proven they'll stay dry for an hour.

The only trick to getting a threaded connection pointing the right direction is to learn how "just barely tight enough" feels through the handle of the wrench. Tighten it that much, then a little more until the fitting is pointing the right direction. Once in a while a particular pair of fittings just really don't want to seal in the orientation that's required. You could try a different fitting, whose threads may have started cutting in at a different place, to see whether it plays nice. I've never had to resort to this but in theory it's an option.

  • Thanks, guys! I hadn't thought of bad threads/fittings. What is "Armstrong" method?
    – DAS
    Jun 24 at 0:37
  • 1
    Sometimes known as "Armstrong-Fawcett" method. A play on words. "strong arm" and "force it"
    – Jasen
    Jun 24 at 7:42
  • There is also the German torque standard: "Gud 'n Tite". Jun 24 at 13:54

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