got fuel?

[banjosail]

Bought a brand new Sea Swirl 18.5 foot with a 115 four stroke Yamaha Last year. I babied the hell out of it using only 26 hours during the whole summer of 2003. I had immediate problems with the fuel gauge which was not showing gas despite my filling it to overflow (on the trailer at alocal gas station).
So I found out that SeaSwirl shippers sent their boats on the long highway trip up north with empty fuel tanks and the sender just a rattling and banging inside the tank. So the dealer said I was not alone in my complaint and when the part finally came in (December) the new fuel sender replaced the old one.
Here is my question:
How do you replace a fuel sender unit? Do you need to pump out the old fuel and then replace the unit? If that is the case, I do believe I have been had.
When I finally took my boat out last week for the first time this year and thought the new sender was malfunctioning because it was reading nearly empty. I called the dealer and he asked if I had topped off my tank. I said I thought he had done this. I remember that there was practically a full tank when I left it for him at the end of the season (because I bought and used some fuel stabilizer to store the boat over the winter months). Anyway, the good news was that the new sender is working after all because I was nearly out of fuel...I went out and "topped it off" with 25 gallons of fuel! The bad news is it cost me fifty dollars plus the loss of the original 25 gallons or so of the original fuel which the dealer must have pumped off to work replacing the sender unit. Unless there is another way of replacing the sender. I sure would like to know where that gas went! I'd like to hear before I go back to the dealer with this.