I assume this is a FI type tank, and you drained it through the fuel line connection at the bottom? If so then do yourself a favor and drop the tank so you can remove the destroyed "filter" screen that is inside. It is a fine mesh sock that fits over the fuel supply tube and the screen becomes clogged with gunk and/or otherwise rots. That restricts the fuel flow significantly, which is why it took three hours for three gallons to drain out. You may not get sufficient fuel flow for the engine to fun properly.
Here is what the "filter" sock looks like when new. This example is for a carb X, but it is the same sock...only located inside the bottom of the fuel tank on the pickup tube:
View attachment 61984
Once the tank is out you will also be able to see a ton of thick gooey "tar" crap coating the lower portion of the tank. It does not come out with normal draining and needs some strong solvent or even acid to remove it. However it will eventually come out and contaminate the entire fuel system, destroying everything. More work now, but a lot less later.
EDIT: I just saw your other thread about draining and cleaning the fuel system. Sorry, I had not come across that thread earlier so some of my comments above do not apply.