Abstract: The invention is a system (10, 110) for regulating volume in a retention cuff/balloon (20) in an indwelling catheter; i.e., the combination of fixed-volume inflatable retention cuff mountable on a patient proximal end of an indwelling catheter (14) and relief valve (23, 123) connected to the cuff. The relief valve has ends for selective introduction of fluid to the cuff and for connection to an inflation tube. A valve port (24, 124) permits escape of excess fluid when a maximum cuff volume has been exceeded, and inflation tube (22) connects cuff (20) to the relief valve. The inflation tube has ends in fluid-tight connection to an interior of the cuff, and the relief valve to thereby permit the cuff and valve to be in fluid communication with each other for selective filling of the cuff to insert and safely retain an indwelling catheter in a patient for an extended period.