Did you draw a water line in your sump? When i had my 45, I did not have an ATO. I did, however, have a piece of tape on the outside marking the ideal waterlevel for my sump. All my sitter had to do was fill it to the line. Never had problems :)
Another thing is that I premeasured the daily food. There was literally no chance of him accidentally overfeeding...unless he decided to be an ass and go through more pre-measured packets LOL I stored them in a pillbox. It was very easy and less daunting for the sitter (he was 12)