A chemical toilet is a toilet which uses chemicals to deodorize the waste instead of storing it in a hole or piping it away to a sewage treatment plant. Common types include aircraft lavatory, some passenger train toilets and the portable toilets used on construction sites and at large gatherings. They can normally be identified with a blue-colored dye in the bowl water. Because chemical toilets are usually used for short term periods and because of their high purchase prices, they are mostly rented rather than bought often including servicing and cleaning.
In the past, disinfection was generally carried out by mixing formaldehyde, bleach or similar chemicals with the toilet water when flushed. Modern formulations are nitrate based and work biologically.
Since formaldehyde is very irritating to the eyes, ears, skin, nose, and throat, it is being replaced by other proprietary blends such as glutaraldehyde and quaternary ammonium compounds, with non-staining dyes and nature-identical perfume oils. Additionally, enzyme hybrids are sometimes used.