I mostly add air (enough of it, too) to my enemas - it gives me the ability to slosh the liquid around in my colon by rolling from one side to the other repeatedly, really loosening up everything very effectively. Cramps? Sure, but manageable. Most folks seem to have an issue getting the air out and believe me, if you think you're gonna simply poop it out with the rest of the enema water as per usual, think again. It tends to get trapped in nooks & crannies in the colon and that's where the discomfort and misery comes from for most.
However, I have a foolproof method to get the air out - every single time. The trick is to get the air bubbling to be ahead of the enema water. And for that it is imperative that the colon is filled with enough liquid so that the issue becomes a matter of simple closed-flow hydrodynamics. If you only take a small volume and inject air (before or after/during) there won't be enough liquid for the air to bubble up into to get it to the exit, and you can have a hard time getting air out. The process is really simple - you do the following a few times in succession:
1. Lie on your right side, so the air in the ascending colon is displaced by the water flowing down, to bubble up towards the transverse colon.
2. Roll over on to your belly and get into the knee-chest position, butt high up and chest as close to the floor as you can for maximum effect. Massage the transverse colon just under your ribcage from right to left a few times. By this time you may already feel air bubbling up the descending colon towards the rectum, and depending on the pressure you can experience an unintended wet fart escape if your sphincter ain't up for the job....
3. Roll on to your left side to complete the air displacement into the descending colon and towards the sigmoid and rectum.
4. When getting up to ascend the throne, remain bent over to prevent the air from bubbling back up the descending colon, get on the toilet and let it rip. Usually quite a thunderous effort, followed by some enema liquid.
Repeat the whole sequence 3 or 4 times, and the air will be mostly out. You then get rid of the enema liquid as you normally would, save to note that following the above sequence works equally well to get the liquid out too.
And that's it - never failed to work for me, let us know if it does for you.