I like 4 quarts because I don't have to refill it as often. I usually get 3 quarts or maybe a bit more in the first fill. Then when I start over with the next fill, I try to get all 4 quarts in me and then I empty out. When my returns are clear I then go for a larger fill, I fill it with 4 quarts, if I get it all in, I then add another 4 quarts and then I open the clamp up and take as much as I can.
My last enema, I got clear returns quickly, then I got the 4 quarts in me, added another 4 quarts, opened the clamp and then when I felt like I could hold no more, I stopped.
When I emptied my bag, I had 3 quarts left, which meant I got a whole 5 quarts in me, which felt so good. I like very large enemas, it felt so good. I have finally gotten back to 5 quarts and there was no pain, just felt super full. I love that feeling.
I used to have 2, 2 quart open top bags that I hooked up with a y connector. I had to fill them, then empty one, refill the empty one, then open the clamp on the second bag and when it emptied, I would then open the clamp on the bag that was refilled. It was a lot of work and now I just have one bag to refill.