Funny you ask that because I just did mine (watched more than helped) at the shop this morning. The tank does not have to come out, but make sure you are down around a quarter tank full. It looked very easy. He just used a screw drive and hammer to spin the retaining disk about half a turn until it popped off, pulled the old unit out and popped the new one in, then reversed the process with the retaining disk. It took all of about 5 minutes. Now the disclaimer - This was done on a lift at shoulder height, but I would not think it would be much more difficult if you jack up the rear end and do it on your knees.