I had to give myself enemas for at least a year before I was diverted from using my j-pouch. I ordered a regular enema kit from amazon. I had no problems with over filling it. You can tell/feel how much you need. He could also get fleet enemas and use them several times. It doesn't take too much water. It was just cheaper for me to use a regular enema kit. I used my bidet when at home and the kit when we were away from home over night.
I hope all works out well for your husband.