an apparatus is provided suitable for use in draining liquid from inside the human body . the apparatus incorporates two reciprocating pumps and a pair of inlet and outlet valves driven by a common linkage system . one pump draws fluid from a reservoir of additive fluid and mixes the additive with the fluid drawn from the body by the second pump . the mixture is discharged to a common collection means . a pressure sensor terminates the pumping if the fluid pressure in the flow path joining the apparatus with the body becomes abnormal . the apparatus may be mounted externally on the body of the patient and may be driven by a portable source of power . major components may be changed quickly and easily if the flow capacity is to be changed or if a component must be replaced .