Whether I leave the nozzle in or remove it has more to do with the nozzle itself than anything.
A straight nozzle, especially a short one is going to get blown out by the muscle contractions anyway, so I take it out.
If it's a flared nozzle, especially a longer one, it makes a good retention device, and so I usually leave it in.
Once and only once, I have had one 3-inch nozzle with a half-inch flair blow out when the bisacodyl kicked in while I was retaining the third round.
I WAS able to prevent leakage.
Fortunately there was no “giver” it was self-administered, because they would have gotten bonked by the nozzle
One and only one time I had a flexible flared nozzle detach from the bag during injection, and get pulled up inside me. This was during injection of the 4th enema of the session. I called for my husband and got into knee-chest position. My husband could feel it with his hand, but could not get enough fingers around it.
Just as we were planning to go to the Emergency room, the bisacodyl kicked in. I felt it blow out! It was brown water, but it WAS my own poop, so I was the one who had to reach into the toilet and fish it out!
So I am reluctant to give specific advice, but I hope that sharing my experience will help you decide!