Peruvian plumbing leaves something to be desired. There’s always a chance that flushing a toilet will cause it to overflow, so you should avoid putting anything other than human waste into the toilet. Even a small amount of toilet paper can muck up the entire system – that’s why a small, plastic bin is routinely provided for disposing of the paper. This may not seem sanitary, but it is definitely better than the alternative of clogged toilets and flooded floors. A well-run hotel or restaurant, even a cheap one, will empty the bin and clean the toilet daily. In rural areas, there may be just a rickety wooden outhouse built around a hole in the ground.
Public toilets are rare outside of transportation terminals, restaurants and museums, but restaurants will generally let travelers use a restroom (sometimes for a charge). Those in terminals usually have an attendant who will charge you about S0.75 to enter and then give you a few sheets of toilet paper. Public restrooms frequently run out of toilet paper, so always carry extra.