If there is blood in the line, you will need to flush the catheter sooner with 20 ml of normal saline. You will need to use two 10 ml normal saline syringes. You must flush your catheter using the start and stop method. The start and stop method is when you start pushing the saline into the catheter and then stop. Push 1 ml, and then stop. Repeat this giving 1 ml at a time until both syringes are given.