Plumbing vents are rarely if ever sheltered. The vent section of the plumbing stack is just as water tight as the waste part, or it's supposed to be. What is this,"U" joint you're speaking about? Is this a trap? Posting a picture would help. Ron

Gents, Thanks for the post and suggestion. I found this articles validates what you guys suggesting me http://www.familyhandyman.com/plumbing/repair/how-to-join-dissimilar-pipes/view-all . I'm very nervous right now with the time bomb dresser coupling ahead my kitchen. I have another question. I plan to change the pipe the whole house in a couple of months. I will do stop-gap solution by changing the PVC dresser coupling to a steel coupling per your advice. My other question is, what type should I change to when it's time to change for the entire house, there are a bunch of them out there. 1) PEX 2) CPVC 3) PPVC 4) Copper Please give suggestion what and why. Our home is over 40 years old, 2 adults and 2 dogs living in 1800 sqft home. Thanks.

Do you mean the whole stack or just a section of that vertical run? If the upper part of that elbow is wedged between the wall and the lower cast stack and doesn't appear to be held up by anything (riser clamps), it is probably only held up by the bottom portion of the stack. A lot of houses did not get the luxury of riser clamps so they are pretty dangerous to mess with. The amount of weight cast iron has makes me a bit paranoid on vertical runs, safety is important. You are looking at probably 300+ lbs of metal that could fall on you. To replace the whole stack, it is a big job. Cast iron makes less water noise, but the slight noise the PVC makes doesn't bother me. Also PVC is easier to add on to in the future and weighs less. 'If' the upper part is supported then maybe just replace a section of that area and convert to PVC there to make it work. If the whole thing needs to be removed, start at the top and work your way down so it doesn't fall on you. Chain breaker is best option. If the cast is in a tight area and you cant get the chain around it the 2nd option is angle grinder with cut off wheel (breathing protection, hearing protection, face shield). Cut out an area in the front of the cast so you can get the grinder in there and work on the back. You would need a person to try to lift the stack above or support it with a riser clamp while you cut below.

Jake- here’s the photo. Your last comments about how to correct did not show up in my feed before the plumber came back. Not sure what that was about except we had horrible internet service the last few days. I did ask to avoid elbow so there would not be a restriction beyond what the PEX already does coming from copper line. So I missed your point about that completely. I was just going from what I read on other forums. He’s added some pre-made supports inside the holes in the wood so the tube isn’t moving back and forth on the wood. And added some tape as well. We are able to get to this pretty easily from the back side of the wall just taking off sheetrock. The valve is installed correctly. And I have not corrected the wires yet on that box. There appears to be enough slack to fix in place. I Also need to check to see if I need a 2x4 below that wiring. Anybody know?