A bench model was created to measure and analyze pressures in a simulated bladder and an actual urine drainage system. Fluid-filled dependent (generally U-shaped) loops in the urine drainage tubing generated back-pressure (in units of cm H2O), directly related to the difference in fluid meniscus heights (in units of cm) across the dependent loop that interfered with emptying of the simulated bladder. If the results obtained with a simulated bladder occur in actual bladders with indwelling urinary catheters, retained urine volume (that can promote urinary tract infection) will increase with larger differences in meniscus heights across the dependent loop due to increased back-pressure. Dependent loops in urine drainage tubing should be avoided. If the dependent loops cannot be avoided or a configuration without dependent loops cannot be maintained, they should be routinely emptied of urine, especially if the bag-side meniscus is higher than the bladder-side meniscus.