I had combined enemas and e-stim numerous times. I find that sometimes E-stim amplifies the sensations associated with enemas, such as feeling of fullness, stretching and urge, and sometimes it overrides them. My “experiments” usually involved some kind of penis electrode (adhesive, wrapped around or inserted), and various electrodes placed on buttocks, or anal/rectal ones. In some instances, I would use a double balloon retention nozzle for an enema, while at the same time place adhesive conductive pads on the buttocks to complete the circuit with a penis electrode. Placing the pads closer to or further away from the anal area would produce somewhat different sensations. A different option would be to give myself a 2-3 qt. enema, then insert a conductive butt plug electrode, again, in combination with some sort of penis electrode. Yet another way to combine the two, literally, would be to use a 10-12 in. length of conductive tubing (with a matching connector), attached to the end of the enema hose as a nozzle to fill with water. Since the diameter of the tubing is relatively small, it creates a rather intense, concentrated sensation in the anal/rectal area, that also varies depending on how deep you insert it. In all of these scenarios, I find the combination of sensations from an enema and e-stim in the rectal/anal/pelvic area extremely enjoyable.
I don't recall ever leaking and making a mess during any of my “combo” play sessions. Still, I usually use a towel as a precaution, and mostly include an e-stim play on the second or third enema fill, when my colon is mostly cleaned out. A colon filled with water does seem to be more conductive of electricity, and sometimes the e-stim sensations radiate into adjacent areas, but I don't find that unpleasant. Also, I only use plain water during such “combined” play.
It seems to me that if you have two distinct activities that you enjoy, it's only logical that at some point you would think of combining them.