I’m sure this is old news, but after reading about counter pressure for filling bottles from a keg, I got this idea. Where the racking cane meets the tubing I quite often got bubbles that wouldn’t go unless I added more pressure to the carboy through the second nipple on the cap (used a small hand pump.) Instead, yesterday I tried hooking my CO2 up to it and it worked great. Kept the pressure down around 2 or 3 pounds to keep the cap from popping off. No O2 gets into the carboy and it self primes. After the keg was full, I put my bottling wand on the end and filled some bottles.
The big rubber band around the carboy does a great job of keeping the cane from moving.