Bathroom Vanity Replumbing Questions

[Carson1919]

Hello everyone, newish to the forum but learning a ton during my remodel via the old posts and internet. Anyways I ran into a snag. I am redoing my bathroom and have a ranch house with an unfinished basement. All plumbing is accessible from the basement. I have an existing galvanized 1.5" laboratory drain that is 3/4 full of crud that I want to replace. I drew up some existing photos to show the layout and what not. Here are my three options I come up with but would like advise:

Option 1:
Cut an access hole on the backside of the stack, attempt to unthread the existing galvanized pipe. If I can get it out, replace with PVC threaded fitting and run new 1.5" PVC line in existing spot. This seems easy in theory but I'm worried about unthreading existing pipe and also would rather not patch the hole to access the bushing. I also would not have access to tie in point in future. This line is 5' to the stack so it provides the vent. I would rather not use a shield coupler if I don't have too.

Option 2:
Run a new 1.5" line to the 2" shower line. Tie into the shower line with a 2" combo wye and add a AAV underneath the sink. This would then give me a vent and new drain line, however, it sounds like most people do not like the AAV.

Option 3:

Run a new 1.5" line to the 2" shower line and tie into the shower line with a combo wye. The run a "island vent" behind the drywall and couple this into the existing 1.5" galvanized line for the vent. This seems like the best solution to me as long as this will provide the proper vent and drainage for the sink.

Thoughts?

 

[WorthFlorida]

It a little hard to understand your configuration. Some pictures would help with the existing. The existing drawing shows a 3" ABS stack. Was this recently changed from iron pipe?
To undo a 50+ year old galvanized pipe can take some doing. Usually you'll need two pipe wrenches. It's alway handy to have one 12" pipe wrench in the tool box. The second one may need to be larger and might be worth renting one, say a 16". You'll need two so you don't move or damage pipe past the fitting you want to open.
AAV's are no issue. I have at least four of them in my home built in 2007. At least one roof vent is required to use AAV's. So adding one for the sink is not an issue.

 

[Sponsor]

 

[Carson1919]

It a little hard to understand your configuration. Some pictures would help with the existing. The existing drawing shows a 3" ABS stack. Was this recently changed from iron pipe?
To undo a 50+ year old galvanized pipe can take some doing. Usually you'll need two pipe wrenches. It's alway handy to have one 12" pipe wrench in the tool box. The second one may need to be larger and might be worth renting one, say a 16". You'll need two so you don't move or damage pipe past the fitting you want to open.
AAV's are no issue. I have at least four of them in my home built in 2007. At least one roof vent is required to use AAV's. So adding one for the sink is not an issue.

The original cast iron stack was replaced with ABS to the main floor joist before I bought the house. I'm guessing this was done in 2015 during the pervious owners shower remodel.

I am worried that I will not get the galvanized unthreaded with option 1 and that is why I'd rather do option 2 or 3. I think it will give me less trouble. I am not opposed to the AAV but I read a lot of plumbers don't like them. I have room to install one, but want to do what is right. That is where I came up with option 3.. My preference is option 3, but option 2 seems easiest..

With option 2, do i just install a 90 sweep in the wall instead of a sanitary tee and just cap the galvanized line with a mission band with cap on the other end?

 

[Carson1919]

Here are two better diagrams of what I am proposing for option 2 and 3. I am leaning towards the AAV with a cap on the old galvanized drain line. The loop vent doesn't seem like any better of an option to me but maybe someone else has a differing opinion?