trouble soldering copper pipe

[AuntieL]

I have to installed a thermal expansion tank to the cold water line leading to the hot water tank. I shut off the water and drained the hot water tank, following tank instructions. and drained the hot and cold water lines. I cut the cold water pipe in order to solder a tee for the expansion tank. After preparing the pipes for soldering I tried to solder the pipe, but there appears to be a littles water in the line that I can't get out and the tee connector won't heat up enough to solder the pipe. I once heard that putting a piece of white bread in the copper pipe would allow the connector to heat up. and that the bread would dissolve in the line and come out when I turn on the water, However, if this is true when I turn the water back on the bread would go into the expansion tank or bypass it and go into the water heater.
What else can I do to get these pipes soldered when there is water in the line??
Any help would be appreciated.
Thanks

[driz]

I always used the bread.

Beyond that I don't; know what to tell you. I had a similar problem with a long drop in my basement once and even the bread wouldn't hold back the drip. I had to drag the tanks into the basement and use my number 6 rosebud on it and you sure don't want to do that. A bigger piece of harder bread shoved further back in if possible maby? It doesn't take muich water to ruin your joint and using the new leadless solder makes it all that much harder. Thats what I did in my problem area. Hell one joint isn't going to hurt anybody either way and its a lot more forgiving to work with.