10 POINTS! I work for free for a half hour to forty-five minutes every shift. Help?

Heya, so I work at a care home as a dietary-aide, which basically means I wash the dishes and do everything else in the kitchen but cook the actual meals. My usual shift begins at 2:30 PM and ends at 7:00 PM so I have to make sure I clock out on time whether I am finished with my work or not. Here's the thing though, I have to wash dishes for thirty people (and it's not just a plate, a cup and a fork for each person either) using very outdated equipment. Not that I mind it just doesn't exactly help with the speed issue. So it takes a while, maybe fifty minutes or forty. But usually the last meal of the day, all the dishes come in at about 6:30 PM sometimes later, giving me a half an hour to wash dishes, mop up the floors, take my garbage out, take care of the coffee station, and all the other odd things I have to do to make sure things are ready for breakfast right away in the morning. So I'm still there at seven, the dishes are not done, but after seven I am not getting paid for the work I am doing, but I can't leave that mess for the morning shift or breakfast will be a disaster and the whole building suffers. So I can't just leave at seven. So what do I do? this is seriously degrading and it's not like I am working slow here, I am running around like a headless chicken and now we are getting a higher census for the building but I am still not getting more time to get my mandatory work done. Please help. Thank you!!