No, enemas or bowel emptying is not necessary.  Although you do have to be careful that feces does not plug the catheter tube.  To help prevent this do not push the tube more than a half inch beyond the sphincter muscle. This will also facilitate quick removal in case of severe bloating, which is common with the first few treatments.

Also remember to use a water based lubricant like KY for the catheter.  Never use a petroleum based lubricant like Vaseline as they do not react well with oxidizers like oxygen and ozone.