I was trying find the right place to post this, but it is about capacity, so here goes. When I first met my partner she was very much into anal play, and had memories of being given Fleet enemas a few times as a child which she agrees might have been a trigger for her enjoyment of things anal. I gave her the first enema she received as an adult, which was with a large custom nozzle and an Ez-Em bag. It went pretty well, but she did say the amount of water was a bit much. Then she discovered Fleet Naturals, which sadly are no longer made. We got them in case quantities, she loved the solution, and pretty soon would be wanting me to give 8 or more at a time. She really liked that she could retain them for very long periods of time, through multiple orgasms. She says she loves taking them and holding them, but says she could do without expelling. For that reason she does enjoy closed system colonics.
After the initial concern about volume, and after the Fleets were gone it has been back to bag and douche syringe enemas. After I first introduced her to my douche syringe with the smooth black nozzle that has been her choice to give and receive. To my amazement she quickly got up to three quarts plus capacity, and just keeps wanting to continue the filling, so she may have gotten to the "gallon cub" a time or two. First couple of times she got very full she experienced some nausea, but now, to my amazement, I have seen her hold these very large enemas for extended,periods with multiple powerful orgasms. I've even seen her fall asleep with over two quarts inside.
I assume she knows when to say stop, but there have been a couple of times when I've backed off because I felt she had taken enought.
But then in the 70's a knew a fairly trim woman who was 4'11" who could take a gallon, so perhaps I am overly concerned.