I have a two story house. I have added an additional circuit for the garage. To get the romex from the panel to the garage... the romex is run up into the second story attic and then down from the attic to the attached garage wall along side an ABS vent pipe. Are their any code issues with having the romex run along side the ABS? In my situation it is a convenient way to get the wire to where I want it. I have no idea what to do about the stapling the romex every x feet requirement.

Since I plan to surface mount RMC in the garage I surface mounted a metal junction box to the drywall inside of the garage and just passed the romex through a hole in the drywall, through one the knockouts, into the junction box. I used an appropriate connector to secure the romex to the junction box. Is this OK? What I am concerned about is if I was supposed to put the junction box in the wall (there really isn't space) and then attach some kind of extension box to it so I could attach the RMC to the extension box.

This will be inspected, but I would prefer to get it right the first time.

Thank you,

As long as the cable cannot be damaged, it can be surface mounted, stapled 12 inch from each box and every 4.5 feet.

Not really following you with the JB issue, you don't need a JB just to leave the garage space and pass through the drywall into the attic.

The inspector should ask for fire caulking to be used at any penetration through the garage wall surface into another space.

I must not have done a good job of describing.

The cable from the attic (2 floors up) to the garage will run inside the finished wall of a second story room to get from the attic to a wall of my garage on the first floor. So, there will be an 8ft run (the height of the room) where the cable will not be attached to anything. Or, am I supposed to open up the wall in my second floor room just to affix the romex to a stud?

The romex will go through the double top plate of the garage wall. If I understand correctly, you are then saying I can just pass the romex through a hole in the garage wall into the back of my surface mounted junction box. Correct?

Adding a circuit wire inside an existing wall does not require you open the wall to affix it yo a stud.