need advice on leaking valve connection

[littleanna]

I hired a handyman yesterday to change out my kitchen faucet, valves, and lines. After he left, I noticed that the dual output/hot water valve was leaking at the connection to the 3/8" copper pipe going to the dishwasher. I think it's a compression fitting.
Any advice on how to correct this? He's coming back today to do some other work, and I really need this fixed correctly, by the end of the day. My dad has cancer and I have to leave town for a while to be with him.
Also, looks like he had to pull some (3-4 inches) of the copper pipe out from behind the cabinet to get it to reach the new valve outlet. Should I be concerned at all about this, that it may have compromised the connection to the dishwasher? How much extra pipe is coiled up behind the dishwasher? So far, I ran the dishwasher and saw no obvious leaks.
Thanks for helping me in a pinch!

[Uncle Cracker]

If the leaking connection is in conjunction with a copper tube, it may just be a matter of using some plumber's rouge or emery cloth to burnish the tubing before making the joint. You don't want to rough the tubing up, but just to polish it smoothly. Scale, particularly on a connection to existing copper tubing, can make for a leaky joint, although it will sometimes stop leaking on its own. There can be any number of other causes (a ding in the ferrule bead, a scratched mating surface in fitting or nut, or a backwards installation of a one-way bead, to name a few...).

More important is the "handyman" and his attention to detail. He should check the joints and not leave you with a bad one. Your satisfaction should be his primary focus.