So I've been testing the pumping waters this week and finally feel like I may have it semi-figured out! I ended up going through 3 different size flanges and settled on 21mm. I've only practiced single pumping so far but I rigged up my hair ties today for some double action. I got 3 ounces! Considering I was barely covering the bottom of the bottle last week I am super excited! I'm hoping I can keep it up. Just wanted to share.