Potty question for four year olds... any tips to get them to clean up well after potty use?

my son just turned four, I still clean him up after number 2. Since he just turned four on Monday, I want to start training him to clean up himself, of course. I am really worried about sanitary problems. The only time he has been in overnight care at the hospital, (thank God it was only once), after birthing stay, was when he was a toddler. He had rotavirus, which was, I told contacted from number 2 being ingested somehow. I thought it might have been from a play group, but since then I have been even more careful about because it was a very hard visit, it was very worrisome for me. I know this might play into why I have a hard time letting him clean up himself after potty use, so if you have any tips, ideas or reurance how to know he is cleaning well enough I would really appreciate it. Thanks!