As kids growing up in the nineteen fifties, mom, grandma, and our teenage aunts, all gave us enemas using a two-quart douche/enema bag. The first enema I can remember getting, was from my grandmother, when I was around four or five years old. She was sitting on a bench, against a wall in the bathroom, and I was laying naked across her lap. If I turned my head, I could see the bag hanging on the wall, and its red hose leading to the nozzle buried inside me.
We never knew, how much soapy or rinse water was in the bag, until around age eight. However, in some respects, it really didn't make a difference. Because, as a rule, we had to try an empty the bag. If we couldn't, and asked them to stop, they stopped. However, if they thought we hadn't taken enough, the enema was repeated. Even after we knew how much was in the bag, it didn't change the fact, we had to try and finish it, if we could. That being said, my siblings and I, never really had a problem emptying the bag.
The soapy enemas we received, weren't as large, as the rinse enemas afterwards. They were always a little larger, and if they thought we hadn't taken enough, we got another one. Growing up, I can still remember hearing "Just a little more." More times, than I care to think about, during either a soapy or rinse enema.