Floatation tank

↑A small floatation tank

A floatation tank, also known as an isolation tank, is a sound-proof, light-proof, enclosed tank partially filled with warm, salty water. The water temperature is maintained at body temperature (37 degrees Celsius or 98.6 degrees Fahrenheit). The tank is large enough so that when a bottom or submissive climbs into the tank they can float without their hands, feet or head touching the sides of the tank.

A floatation tank, at least in the world of BDSM, is typically used during sensory deprivation activities. The enclosed nature of the tank muffles or completely blocks sound coming from the outside, excludes all light, and and eliminates air movement which the submissive or bottom might otherwise feel against their skin. The water temperature and, consequently, the air temperature being at natural body temperature will neither feel hot or cold.

All of this creates a neutral environment for a bottom or submissive.

Using salty water in the tank causes the person in the tank to be more buoyant and to thus float higher in the water. This makes it easier for them to keep their mouth above water and decreases any tendency to sink.