I worked as the dishwasher at a senior living facility. (A couple actually.)
It is much more organized than a typical dishwashing job, because the meals are served at a certain time. So, there's a huge amount of dishes at 630/1230/530 (or whenever), but you know it's coming, and you know how many there's going to be. Not like a restaurant, where the rush could occur whenever, people can show up right before closing, etc.
The duties include more than washing dishes. Filling water, setting tables, helping a little with meal prep, other simple tasks like that. However, if you are organized, you will have a ton of spare time. I spent about 3 hours of the 8-hour shift on break, and nobody cared because I was always way ahead of schedule. When people would fill in when I took a day off, they were not nearly as organized, and still had an hour or so of spare time. There's a set amount of work, and a set amount of time, and few surprises.
Most of them will offer you a meal, as there's always leftovers. As mentioned, there are some toxic personalities the gravitate to places like that, but you're not 17, so you should be able to brush them off.