The portable sanitation unit, better known by many other names, including porta john, porta potty, and other trademarked titles, is basically just a small enclosure with a tank for holding waste. It includes some sort of disinfection agent and deodorizing agent, with ventilation in the top, and locking doors. They all include a sitting toilet, and many have a urinal, as well. A standard addition is toilet paper and a dispenser.
Of course, when considering porta potty rentals, it's important to realize more is necessary than just the actual toilet. The washing facilities are a necessary part. Your rental company can provide those, as well. You could go with something simple, like a dispenser for hand sanitizer, but many companies will offer actual washing stations. A foot pump can provide water, and soap and towels can be provided. In fact, you could even go all out and get a warm water washing station, but that will likely require a source of power at added cost.
Sometimes, a permanent bathroom is just not feasible. Outdoor events will only last a few days, and construction sites will only be worksites for a year or so before they have their own restrooms. A portable sanitation unit can serve ten people during a full 40-hour work week without cleaning. And speaking of cleaning, that comes with the cost of porta potty rentals. The company will do all the cleaning, disinfecting, and draining at least once a week, and possibly more. Make sure to ask about that when renting for a long-term project.
The porta potty is, of course, portable. If you need to move it elsewhere, it can just be loaded into the back of a pickup truck and taken wherever you need it. In fact, there are special construction site units just for high-rise sites. Hook it with a crane to move it to any floor it might be needed, or roll it to different sections on its installed casters. Whatever your needs, there's a unit that can fill them.
An outdoor event can easily require a large number of units. You'll need more than the standard type of accommodations. For instance, what about those who need wheelchair access? Luckily, there are units for that. You might even choose to go for all the amenities, offering trailers that have sinks with running water, and even mirrors, just like a stationary rental. With so many choices available when it comes to porta potty rentals, the real difficulty may not be in providing restrooms - it might be in making the choice of what kind you want to have for your site or event.