Slopping out is a kind of bathroom situation where people who live in a prison or a shared living space do not have their own private toilets or bathrooms. It means that instead of using a private bathroom, people have to use a bucket to do their business, and then the bucket is emptied and cleaned by someone else.
It's kind of like when you have to go potty at a park and there's only a big porter potty to use, but imagine having to use it all the time and sharing it with other people. It's not very pleasant or comfortable. People who have to slop out don't have a lot of privacy or dignity and might feel embarrassed or ashamed about it.
Most people think that living conditions like slopping out are not okay and that everyone deserves basic human rights to have clean and private spaces to do things like go to the bathroom. Thankfully, organizations and groups work towards improving the living conditions of people who have to slop out, and hopefully, someday everyone can have their own private bathrooms.