Mixed feelings here. Generally I wouldn't recommend douching or enemas to begin with, but if you are going to I would probably recommend water unless you know what's in the enema fluid you buy. Some kits contain laxatives that induce shitting (because for real am I going to say defecation?) while others are for more gentle cleaning. As with anything, know what you're putting in your body before you put it in. The rectal lining is fairly permeable to chemicals and things since a huge part of the lower colon's function is reabsorbing water (this why being on the receiving end of unprotected anal sex is one of the riskiest behaviors for exposing yourself to STIs).
Sometimes after I masturbate my penis stings for a little while, like in the urethra. Eventually it goes away and I have tested negative for any diseases. It only happens sometimes. Does this ever happen to you? Do you know what I'm talking about? Should I see a doctor?
This is one of those questions where I repeat several times that if you aren't sure and are still concerned, go see a medical professional.