A Foley catheter is a thin, sterile tube inserted into your bladder to drain urine. Because it can be left in place in the bladder for a period of time, it is also called an indwelling catheter. It is held in place with a balloon at the end, which is filled with sterile water to hold it in place. The urine drains into a bag and can then be taken from an outlet device to be drained. Laboratory tests can be conducted on your urine to look for infection, blood, muscle breakdown, crystals, electrolytes, and kidney function. The procedure to insert a catheter is called catheterization.