Yeah i wasn't really too worried about that particular fitting and the potential leak of sewer gasses. There are two reducer fittings associated with the vent section, and there is one reducer fitting in the drain section. The reducer in the drain was the one that I was more concerned about. But I also know that those couplings are larger, and therefore the sticker covers less relative are, so hopefully there is plenty of plastic to plastic welded area. I'm going to assume so, because today it got buried under concrete, and I have no plan to rent another jack hammer.
I was more annoyed than anything. I've spent the last 4-5 days learning all about plumbing and when to use sanitary tees, vs wye tees, vs double fixture fittings, etc. I spent a lot of time planning this out, making sure that my new bathroom plumbing work first attempt and will serve me well for a long time to come. And then when i saw that my friend didn't take 30 extra seconds to remove the sticker that could obviously weaken the weld, i was pretty annoyed. Today, without my asking, he removed that one section and replaced it, which was nice of him... but i wasn't going to worry about it too much further.
Anywho, last night i decided to do a little experiment to see what a weld on top of a sticker might do. Firstly, i found an extra reducer fitting. I noticed that the sticker covers 3/4 of a 2 to 1.5 reducer fitting section. That leaves a potential of 1/4 of the reducer to still complete the weld, which should be okay for the most part i would think. (but still annoying!)
I then grabbed an extra sani-t, with an exposed sticker. I cut some larger diameter pipe into two small sections. I applied glue to the piece of large pipe and the sticker and stuck them together. I then applied glue to the other piece of large pipe and a different section of the sani-t, sans sticker, and glued them together. I let it sit up over night. In the photo below, the section glued to the sticker is on top, the section glued directly to the abs is on bottom.
The next morning I tried taking them apart. The good news is that the glue stuck to the sticker pretty good. The bad news is that the sticker ripped right in half easily, and came off the sani-t without much of a fight. As is suspected would happen.
The other glued section without the sticker between was incredibly strong. Try as i might, i could not tear them apart. Thus confirms the fear that there will be NO WELD between the two sections of abs where the sticker is left between them. Of course I'm not saying that any coupling welded together with a sticker left in there is doomed to failure, but I would certainly say that is a sub-par welding job, and it should always be worth ones time to make sure that there is no sticker or other paper or debris stuck between two sections of pipe before welding.
Tomorrow i'll try to bust apart the old fitting between the sani-t and reducer coupling. If i seen anything interesting I'll post up the results.