John,

"What Mike is eluding to, but being deliberately evasive for whatever reason, is that the base flashing skirt can not extend into the valley, can cause water intrusion."

I don't agree with that. I read Mike's response as "the problem of the slow drain rate has an origin other than the vent height".

"You can have a vent that height, HOWEVER, it may also indicate previous plumbing repairs for bad venting or drainage which I think is what you were driving at in your origional question that no one answered for you. Tell your client to consult with homeowner if there were any previous repairs. Did you see any problems with the drainage to tubs, sinks in that area?"

What am I missing? All three questions were answered.

I sure wish people would just answer questions directly, state why things are or are not a problem, and then just provide the proper recommendation. It would stop a lot of nonsense on this board