Take up an amount of Hepes buffered medium in the tip of the transfer pipette, then make a small bubble by taking up a little air. Then take up some more medium - roughly the same volume as the air bubble, then another air bubble, same size as before. Then take up about 2-3 cm of buffered media and then a tiny air bubble once more. Take your embryos in the smallest possible volume of medium, lining them up side by side in the transfer pipette. Introduce another tiny air bubble when all the eggs are loaded.
Some people use mineral oil instead of or in conjunction with air bubbles for pressure control.
Once the pipette is loaded and the uterus positioned, move the petri dish lid supporting the mouse to the microscope and turn on the overhead light source. Once the lights and focus have been adjusted and the mouse positioned to suit yourself, use the pattern 55 superfine forceps to gently tear open a small hole in the transparent bursa membrane at the point btween the ovary and oviduct where the infundibulum is located. Take care to avoid rupturing the small capillaries that run across the bursa as these will obscure your view of the infundibulum. Once there is a hole of sufficient size to reach the infundibulum, grasp it at the end with one pair of pattern 55 forceps while inserting one blade of the other set into the tube itself. This will ensure that the mouth of the infundibulum will be open and accessible to your transfer pipette.