Need to repair a hole in plastic gas tank. What is most common type of plastic for gas tanks?

I was working on my 1988 Yamaha 570 Exciter this weekend and accidentally drilled a 1/8" hole in the bottom of the plastic gas tank. I tried using some two part epoxy putty to fill in the hole without success. I also tried plugging the hole with a bolt without success. I have a plastic welder and plan on using it to try to fill the hole next; however, I do not know what type of plastic it is made from. I am leaning towards polyethylene but am not sure. If any one knows, or has any ideas for a repair I would appreciate them as the tank has been discontinued. Thank you.