One thing you may have to consider too is issues that may arise putting a 3" pipe in an outside wall that is 8" thick. I used to pour basement foundations and NEVER (at least in my area) did I see plumbing vertical in an outside wall. Will this cause an engineering issue (i.e. - load) and if so you would now be liable for foundation cracks, leaks, or worse. I could be off, but check with local foundation companies to see if they know if this is acceptable or even common practice and see if there is a procedure you would need to follow.

Also you will need to plan on being there as they install the forms because that can happen very quickly and chances are they won't stop and wait for you. Not sure how you are going to seal the end of your pipe to the form either, I don't envy you on this one!