Originally Posted by bryce
So, about these dissimilar metals can i just put something between them?
If you put plastic against the vent pipe where it exits the W.H., make sure your homeowners fire insurance policy is paid up and current. Shouldn't take too long to burn the place down. Hopefully, not while you're upstairs, sleeping soundly.
Best thing to put between the two metals is an air gap. Wider the better. What shows in the picture appears to be touching, at one of the raised joint elbow adjustment rings.
As others have so eloquently said--your plumber is a (definite) hack.