there's a 17-19mm bolt (can't remember) on the left rear of the tank. most likely it is covered in undercoating. So you'll probebly have to scrape that off with a wire brush or flat screwdriver.
have a pan under, it comes out fast!
when it starts to look like you're getting close to draining it all, jack up the front right corner of the car.
that will cause more gas to go to the corner of the tank with the drain plug.
I was told that the EG was the first gen civic to have this handy feature
Edit: EF's also have this. Thanks for the update