My early enemas were all with a bulb. Even now I use the bulb from time to time when I am in a hurry or just need a quick flush of the bottom end. I know from experience it takes an average of 16 single-handed squeezes of an 8 ounce bulb to inject 2 quarts, therefore averaging only 4 ounces delivered per bulb squeeze. Yes, I know if you squeeze with both hands you can get more, but that is not how I learned from my mom.
When I was a little kid, most times I only got a bulb or two, so not much. Mom never forced more on me when I said I was full but it was understood if it did not bring a good poop it would be repeated with more. Only a few times was it repeated.
By time I was ten or so, I started giving myself enemas and sometimes tried to see how much I could hold but usually quit after 6-8 squirts which was only about a quart delivered.
The only bag enemas I got as a kid were a couple from grandma when I was ten. I remember feeling very full with only about a half of a bag, or about a quart.
I was an adult and married before I bought my own bag and started a deliberate plan to learn to take a full 2 quart bag. It took several tries before I was successful, learning that sometimes when the cramps come you just have to clamp off and tough it out rather than heading for the toilet. After a few minutes the cramps subside and the remainder of the bag goes in easily.
That being said, after all these years I still do not enjoy enemas of more than about 2-1/2 quarts. 3 quarts is about my limit. I want to enjoy my enemas, therefore I stop when I feel uncomfortable and it is no longer fun.