You don't say if your boat is hauled or in the water. If it is in the water, the above suggestions are all good.
If however, you are now hauled with a full tank, then I have a solution for you.
Disclaimer: I personally have not done this, but a good friend at my yard was hauled for hurricane Irene and never re-launched. Thus he had a half-full tank. Here is how he emptied it-
He got a 5 gallon bucket, a good pair of rubber gloves, and a rock. He stood under the over-board outlet thru-hull and holding the bucket close to the hull, he tapped on the hull with the rock. His wife turned on the maserator pump. When the bucket was nearly full, he tapped on the hull again with the rock and his wife shut off the maserator. He then transferred the bucket contents to another container and continued the process until the tank was empty. He then flushed the tank with a few gallons of water and winterized per his normal procedure.
There was one point where the process nearly turned into a disaster. After the maserator was started and the bucket was filling, he dropped his rock. Fortunately his wife heard the frantic pounding on the hull and shut off the maserator.
I suggested that if he needs to perform this feat another time that he get a better means of communication. I only wish I had been present- a picture and the story would have been great to have for our power squadron newsletter!