Hi! I’m watching a rabbit for a little and I need help with diet issues.

He had diarrhea earlier today (first day of bunny sitting), which was quite concerning. The owner said he was having digestive issues from too many treats, so I had expected some extra soft poos from the rich diet (I used to have a rabbit, so I know a little about poo). However, this was actual watery stuff that was puddled onto his fur – which I had never seen in a rabbit. I gave him a butt bath and he seems to be doing okay now (drinking and eating).

My question is mostly about how to get him to eat hay. I have some hay for him, but he only eats pellets (I’ve watched him before and he’s always been that way). It’s not my rabbit, so normally I wouldn’t worry too much about changing the diet, but I know hay is super important for bunny tummies. I also don’t want to just take away the pellets, in case he still refuses to eat the hay (I figure no food won’t be good for his belly either). 

So do you have any tips and tricks for making hay more appealing?