A subcutaneous ureteral bypass (SUB) was placed in a 10-year-old Birman cat for management of unilateral ureterolithiasis. Perioperative occlusion of the nephrostomy tube of the SUB device happened secondary to a severe pyonephrosis. Flushing of the system throught the subcutaneous shunting port was made with saline solution after clamping the urinary bladder catheter. Repetitive flushing of the device was performed daily for 3 days to be sure of the remanent patency of the catheter. Repetitive flushing of the SUB device is a successful renal-sparing treatment for pyonephrosis in a cat and may be considered as an effective treatment option for this condition.