The Port-a-john, also called a Port-o-let, Sani-Privy, Port-a-san, Porta-Potty, or any of a variety of other trade names, is a modern portable self-contained outhouse manufactured of molded plastic in a variety of colors.

Port-a-johns are large enough for a single occupant, usually about three feet on a side by seven feet tall. They are held upright by the weight of the disinfectant liquid in the holding tank at the bottom. Nearly all include both a seated toilet and a urinal. Most include lockable doors, ventilation near the top, and a stovepipe vent for the holding tank; some newer models include toilet paper or, occasionally, antibacterial hand gel dispensers.

Though more expensive than a standard permanent outdoor latrine, Port-a-johns have several significant benefits, mostly related to their portability. They are rented to customers by companies that guarantee their cleanliness, and so as a rule are drained, cleaned, disinfected and deodorized on a weekly basis. As they are not plumbed, they do not clog or overflow. A single Port-a-john can be hauled in the back of a pick-up truck.

They are frequently seen at outdoor work sites, particularly construction sites, and large banks of dozens of Port-a-johns allow for ready sanitation at large gatherings without long lines for the restroom.

When used alone, Port-a-johns are susceptible to tipping, usually as a prank. The disinfectant and accumulated waste in the holding tank of a Port-a-john generally will hold it upright against fairly stout winds, provided it is on a level surface. Tipping a Port-a-john all the way over onto its side with an occupant inside can be a serious health hazard and may result in a lawsuit.