No you don't have to drop gas tank just drain gastank down put car in the air. Take a punch and remove large nut that holds sending unit in and remove. Keep old nut because most new ones won't work and you will need to use old one to have it seal up. Use new seal and reinstall new unit and fill with gas and chech for leakage. Do a search and you will find lots of photos and how to's in old threads.