yeah 25g is way too small unless you're drawing with vacuum assist like they do at the labs. 16g is what they use at blood drives, but that's way too big and it damages the vein, that's why i went with 18g with vacuum assist via tubing and mouth. don't overthink the sterilization issue, if the needled is new, you're good to go, and the blood is coming out of your vein not going in, so nothing from the tube will ever get near your vein.