Found this on the internet......
Go to the drugstore, try not to look sheepish, and purchase a box of disposable Fleet enema kits. (They're cheap, and if you do it late at night, only you and the cashier will know what you're up to.)
At home, give yourself 20 minutes (or more) of privacy in the bathroom. You can take a bottle of lube with you, which you may/may not need depending on how experienced you are at putting things in your ass. Run the tap so that the water is lukewarm. It shouldn't be hot, or it'll hurt.
Open up your box with the enema kits (I think they usually come with two bottles). Take out one, and now empty the contents down the sink. Some enema kits come pre-filled with saline solution or other stool softeners; these just aren't necessary. Warm water will do the trick.
So, before you do the enema thing, you'll want to make sure you've emptied your bowels first. It just makes things tidier, you know?
Ok, now that's out of the way, fill the bottle with lukewarm water, and reattach the cap. If the tip is pre-lubricated, you're good to go, otherwise apply a little lube to your ass or the enema tip.
Kneel on the floor, or on a towel, or whatever. You want your ass in the air. Now gentle reach around and insert the tip of the enema into your ass. It shouldn't hurt, but don't force it either - it might feel kinda scrapey as it goes in. Once it is inserted, slowly and gently squeeze the enema so that the water enters your rectum. Pull out the enema, and kinda let your body relax. Give it 5 minutes, 10 minutes; you'll know it's time because you'll feel a bit or urgency.
Return to the toilet, and empty yourself. Repeat the process until the water runs clear.
A few further notes about enemas: it's not a good idea to give yourself an enema regularly, as it can irritate the lining of the rectum, and make it drier than it should be naturally. Also, it's best to do this a couple hours before your play session, to give your body a chance to relax and recover.
Once you're done, It is best to follow up with a shower and some gentle soap to the outside of the anus. (No soap inside! Ouchy stingy pain!) Rinse, dry off, and get ready to have fun!
One further side note: you should be using non-glycerine-based lube. (Ie, no Astroglide!) Glycerine breaks down to sugar once in contact with mucous membranes, and where there's sugar, there will be yeast. Ick.