After my first session at the fortress (it was a great time - thanks Mistress Rey), I guess I can answer my own question somewhat. One salt water enema (CVS brand I think) had a decent amount of water. I got three good 3 squirts out of it. You could also unscrew the cap and fill it with regular water. Then I tried one mineral oil enema, also a disposable CVS brand. It was about the same size as the salt water enema, but I think I only got 2 uses. It is safe to use one salt water enema bottl