leaking joint?

I recently soldered in a tee to my 3/4 copper line to install an expansion tank to go along with a PRV. The joint looks filled, but there is not a bead of solder along the outside of the joint. I've been checking periodically for leaks, and every couple days I see a minute trace of water at the bottom of the joint. It's not beading or dripping, and I can barely tell it's there until I wipe it away with the tip of my fingernail. I've soldered bad joints before, and those leaks were VERY apparent. Does this sound like a leak or could it just be condensation (the rest of the pipes are pretty sweaty)? I just wanted to run it by you guys before I redid it. Thanks.

I suspect it is leaking. There must be something that makes you think it's a leak and not condensation, and I doubt that any reassurance to the contrary wouldn't set your mind at ease. I'm sure you know that you can not just add solder to the joint now because water has been present.

I thought it must be a leak but was a bit reluctant to cut it out before I got a little confirmation. Hopefully the next one will stick. Thanks Gary.

I don't know where you live, but sweaty pipes are not good and lead to mold. Run a dehumidifier and see if the joint stays dry before you rip everything apart.