I should elaborate... I'm redoing my entire home (single story ranch) in schedule 40 PVC for DWV. While not required by the inspectors, I want to perform a leak test before putting up sheetrock. For the most part I can either use rubber expansion plugs or plastic test caps (flanged white PVC cap). Obviously the test caps are much cheaper, on the order of 20 cents vs. $2-4 for the rubber plugs.
So I'll primer and glue them in place. I just assumed when properly glued, after they are knocked out a little ring/flange will remain in the pipe's ID. The toilet flange already has a knockout built-in.
I have one tricky spot to try and block off and I'm not sure how to do it. It is a 3" combo where the vertical main stack ties in and horizontally thru a fernco coupler ties to the cast iron pipe in the foundation. Since its all assembled/glued/secured I cannot pull the combo away from the fernco coupler.
What can I use inside the combo (has a cleanout on the end) to block it off? Otherwise the water will just run out into the sewer line.