The container ends up almost overflowing when adding that volume, which makes removing air pockets tricky if it's not oversized. Should some liquid not fit inside, remember the amount of sterile water added so the concentration can be adjusted later. Watch the rubber seal when loading the pen refills so it doesn't pop loose from pressure. Because the filtering happens straight into the pens, I limit each to about two milliliters for simplicity and use additional sterile water to clean the source container before mixing into the end containers, like dividing the initial two into one each then using one more to rinse and divide half and half. This way two separate ones mean I can avoid repeating on the same pen or container beyond five uses and store the spare cold. Apologies if this makes it more involved. Just stay attentive to the steps taken.