About this "The Simpsons" episode:

The Simpsons - Homer Simpson in: "Kidney Trouble" is the 8th episode of season 10 and number 211 overall in the series.
As the Simpson family is driving home after spending the day at a ghost town tourist attraction, Grampa needs to use the restroom but Homer refuses to stop the car. Grampa is forced to hold his urine in for hours and as a result his kidneys explode. With not much time left for Grampa to live, Homer offers to give his father one of his kidneys. However, he runs away from the hospital out of fear of the procedure and decides to hide, feeling shame for leaving Grampa at the operating table. He joins a group of weird characters on a ship who are also hiding out of shame for things they have done in their lives. However, Homer is rejected even from these outcasts because they are angered and disgusted by what he has done to his father. They throw him into the ocean and he drifts back to Springfield. There, he plans on giving his kidney again, but runs away at the last minute once more. After being knocked out by a car while fleeing from the hospital, Homer unwittingly gives his kidney while unconscious.