Twenty years ago, I could easily handle a gallon. I had two, 2 quart fountian syringes. They were Y'ed together, each had a clamp on them. I hung them from the floor joists in the basement in the 1/2 bath. I had a gallon pitcher that I filled with water, then poured it into each syringe to the top. I then let the air out of the hoses and then I was ready for my enema. I would then re-fill the pitcher with very warm water, so that when one of the syringes was empty, I could re-fill it in case I got both syringes in me. I did that a lot, just wish I had done that earlier in my life, like when I got married, almost 50 years ago.
I was always able to drain both syringes and then refill each one. One day I got 3 full syringes in me. I was huge, I kept doing that two or three times a week. I could feel the warmer water go in me each time. I did this as much as I could. Since the syringes were very high, I got a really great fill each time. I would always start with 2 quarts. Empty myself, then do another two quarts, then if possible add the next 2 quarts. Once I got to 4 quarts, I measured this with the pitcher, I felt great. I tried for more and more. Was I stupid, probably, but I wanted to see how much I could hold.
Finally after doing this for months I was able to start the 4 syringe, 6 quarts and starting the 7 th quart. I thought I was going to burst, but I didn't. I did this for a couple of months, getting 6 full quarts in me and then one day the 7 th quart went in with ease. How and why, I don't know. I was delighted, I was also huge. I looked like I was carrying a child. I did this over and over again, the feeling was wonderful. No pain,, just a huge fullness and I would then expelled all the water. I re-filled myself again. I loved doing this.
I did measure the water with the pitcher. When I finished my enema session, I would drain all the water from the syringes into the pitcher to see how much I had really taken. It was a lot. I tried to get to 8 quarts, but never happened. Got close a numer of times, but pressure took over.
Now today, I am lucky if I can get 2000 ml in me, which is about a half a gallon. There have been rare occasions that I have gotten 3500 ml in me, once a year or so I got 4000 ml, but that was after doing enemas 3 times a week for over 9 months. I was able to do it. Now I am lucky to get the 2000 ml in me. Probably with lots of enemas, I will be able to get back to 3000 ml and just maybe 4000 ml. (a gallon plus)
Those were the good old days, younger and just a touch crazy.