Modern fuels are risky at that age and with that quantity. The alcohol tends to separate unless it has had Sta-Bil added to it and the alcohol absorbs water from the atmosphere and they also gum up really badly in small orifices. I had a boat I had to pull the tank and drain a few years ago, about 1/8 water it seemed (you could see it because the tank was translucent). Small engine carburetors are notorious for gummoing up the idle jets and floats sticking due to old fuel. Not saying it wouldn't work but you might want to consider the drain path and then slowly use the fuel over time blended in with larger quantities of fresh fuel.

 

Today's gasoline, even the expensive non ethanol that will likely test positive for ethanol, has a shelf life of about ,2 weeks to 30 days without a stabilizer being added while it was still fresh.

I love today's gasoline, keeps my shop busy. Doesn't matter if it's a plastic or metal container. Aluminum, stainless, galvanized...fuel goes bad just the same. Plastics just won't corroded or rust.

 

I would not use 5 year old fuel in any engine that I liked.

 

I see the fuel pump as a good way to drain it. There is no rust settled in a plastic tank to clog a filter. And if there was any and the tank is not cleaned when purging the fuel; it will go into the filter later when new fuel is loaded.
I believe a hose is obstructed to insert trough the fill neck as in siphoning from outside ? And I would add in small amounts to the new fuel or use in a mower...

 

Would storing gasoline in 5 gallon buckets with lids be safe? Some places online say it will cause an explosion, others say it is fine. It does get pretty hot here, but it would be stored in a large barn/shop.

 

And by "in a large barn/shop", you mean "OUTSIDE a large barn/shop"!?

 

When I drained the fuel out of my boat I scored a free 55 gallon steel barrel off the local craigslist, kept the fuel in there and dipped it out by hand a gallon at a time and used it in my D2's. 1 gallon in a 20 gallon tank is a lot of dilution and it worked fine. There was about 5 gallons of water at the bottom so when I got down to that level I stopped. Kept in outside in a paved area on the driveway away from everything else of value. Kept a lid on it but not tight so as to create a pressure vessel - normal temperature changes will cause significant pressure changes in a container of gasoline. Never had a problem but always respected the potential fire danger from spark and temperature.