Abstract: Appararus for handling fluent media such as an effluent tanker vehicle or mobile cesspit and gully emptier is provided with a rigid tank divided into two variable volume chambers by a flexible diaphragm enabling one chamber to be used for holding the media, giving a facility for emptying and filling to be effected by pressure transfer across the diaphragm on application of air pressure or vacuum in the other chamber. In this way only the one chamber need be contaminated by the fluent media, the other being kept clean for operating air or transport or clean water or other fluids, and substantially the whole volume of the vessel can serve as either chamber, of which the following is a specification.