Tiny (?) leak in galvy pipe

Hey folks,
I'm working on installing a laundry sink. I tied a couple lengths of galvanized pipe into the existing stubs for the washer hoses. There are 2 new vertical lengths that run a couple feet down, 90 degree elbows, and horizontal lengths running a couple feet over to shutoff valves.
I wrenched all these pipes together (with tape) and turned the water supply back on. No obvious leaks, so I thought I was in good shape. A couple hours later, though, I found that the end of one of the vertical pipes joining into an elbow was very wet. Not enough to drip on the floor, but pooling up around the rim of the elbow itself.
Tightening the vertical pipe into the elbow would loosen it from the tee above, and the pipes are flush against a wall, so I knew I'd have to rip it all apart to fix it properly. It didn't look bad, so I put some towels down until I had time to finish it in a couple days.
Now, a week later, the "leak" has disappeared. The pipes are dry at all the connections. I checked daily since I discovered the problem, and the towel never got wet. The elbow was wet for a couple days, but it dried up soon after.
I don't have much plumbing experience. I don't want to take all this apart if I don't have to, but I don't know how a leak can develop and then disappear. Seems to me once water finds a path, you've got a problem.
So, is there an explanation? Can I ignore the "leak" I saw, or should I bite the bullet and pull all the piping apart to fix it?
-Dave
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If there's a lot of minerals in your water and the leak was very tiny, it could have sealed itself. Keep an eye on it. Plus there are coatings available for sealing leaks, some of them even claim to work underwater. I've never tried them, but I'd try all options before I took on a major disassembly.
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Good chance the leak may never come back. Sometimes a slight leak at the treads will seal from the solids in the water or the pipe dope moving around or in some cases, oxidation is your friend. . Keep an eye on it and if it returns, do it right and take it all apart. No simple fixes.
As long as the pipe is threaded in properly, there is no chance of the pipe just popping apart.
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