I'm very sensitive to glycerin. Frequent use will trigger IBS so, I'm a bit fussy about lube.
I've lost colon tubes from surface cracking by petro jelly. Crisco works per Compacto's posts and I'm getting good life out of my colon and rectal tubes. (Crisco on the first 6")
First enema, a coat of partially dissolved Ivory soap on the length of the tube. Lube shooter injects several cc's of Slippery Stuff(gel). Once the soap starts flowing that's plenty of lube to help the 38fr tube. I've no experience larger than 40 so must defer to others; however, Ivory makes a great lube for the first enema.
Follow-on enemas: renew the Crisco on the tip and apply a coating of Slippery Stuff (gel) along the tube. Again, I use the lube shooter to inject a couple of ml of lube into the rectum. Am now trying a silicone lube and it seems to hold up through two or three high enemas without any need to re-lube the tube. On that basis, it's perhaps cheaper than water based lubes.