What's inside a flushing portable toilet's fresh water tank?

A flushing portable toilet's fresh water tank contains potable water that is pumped to the flush mechanism.

Fresh water versus waste water
A flushing portable toilet has two separate tanks. The fresh water tank holds clean, potable water that supplies the flush valve and, in a deluxe unit, the handwashing sink. The holding tank below collects the waste and flush water. This is the main difference from a standard portable toilet, which has only one tank for waste and relies on gravity and chemical deodorizer.

Tank operation
The fresh water tank is filled by the operator during a service visit. It uses a small electric or manual pump to send water to the toilet bowl when the user pushes a button. The used water and waste then flow into the sealed holding tank. Because the system uses water, it requires more frequent servicing than a standard unit, especially in hot weather or with heavy use.

Service and placement considerations
In cold climates, the fresh water tank is a freeze point. Operators often drain these units for winter or use them only in conditioned spaces. For an event with food and alcohol lasting over four hours for 100 people, a flushing unit provides a more comfortable experience but needs reliable truck access on level ground for weekly service. The driver pumps both the waste from the holding tank and refills the fresh water tank from the truck's onboard supply.

That's the basic setup. Ask if you have specific questions about the plumbing or maintenance.