Your two kidneys clean your blood and get rid of wastes. They contain about a million tiny filters, or nephrons. The waste liquid from your kidneys is called urine. It flows down two tubes, called ureters, into your bladder. When you go to the toilet, it flows out through another tube, called the urethra. A man's urethra is about five times longer than a woman's because it has to reach to the end of his penis.