How to remove bad gas

Would an old school siphon work?

 

The normal way on anything newer is to disconnect the fuel line in the engine bay put a hose on it running it into a gas can and have a scan tool that is advanced enough to turn the fuel pump on. If you can’t get access to a scan tool you might need to just pay someone as the cheapest one I know of is $1000.

 

Sounds to me like your SON needs to pay for a shop visit.....for them to pump the old gas OUT and then see if the roughness still is there.
A close inspection for rodent damage to the wiring would be in order too.

What you did by dumping more than one "additive" into the gas at the same time just made matters worse, not better.
You may need new plugs already.

 

Plenty of cars start the fuel pump as soon as ignition is switched on, so not much of a tool needed beyond the ignition key.

However I don't think the Prius is one of those. The good news is that Toyota Techstream, the gold standard of diagnostic tools for the Prius, is very cheap when bundled with an interface cable on eBay.

Good luck!

 

With the greatest respect for the do-it-yourself approach, I’d like to suggest that de-fueling is a task that, if you have to ask how, you probably shouldn’t do.

Gasoline and gasoline vapors are hazardous; besides the risk of fire and explosion, they are also toxic and carcinogenic. In repair shops, de-fueling is done with portable pumps and tanks made for this purpose, such as those sold by JohnDow Industries and WIS Associates. This equipment is fairly expensive, but JohnDow’s white paper (PDF) explains why it is needed for safety.

There is also the problem of disposing of the old or contaminated gasoline in a safe and environmentally responsible way. A few gallons, in an approved container that you’re willing to surrender, might be accepted as household hazardous waste. Otherwise, it’s an expensive call to a disposal contractor.

If you choose to proceed on your own, be sure to see the warnings and information in the Repair Manual (more info). For example, before disconnecting any part of the fuel system, you must do the procedure for discharging the fuel system pressure. The manual also explains how to use the Active Test feature of a Toyota Techstream diagnostic system to run the fuel pump with the engine off. In this situation, I wouldn’t suggest doing that, however, since you don’t want unserviceable fuel to go through the pump.

Keep in mind that the Repair Manual is written for experienced technicians and doesn’t try to explain all of the hazards or the precautions needed to avoid death, serious personal injury, or property damage.

 

Let's not put the cart before the horse here--you assume it's running rough because of bad gas, but that's just an assumption.

You said the check engine light is on, which means there are trouble codes stored in the computer. Can you limp the car to an Autozone or other parts store? They'll read the codes for free. Post those here and we'll all have a better idea what is actually going on and how to address it. Otherwise we (and you) are just guessing.

 

^ that.

1. If I woke up with your problem, the first thing I would tackle is the CEL (Check Engine Light.) I would drive (my other car) to Walmart, Harbor Freight, or order one off of Amazon. Expect to pay about $20. Anything more than that is probably wasted money since you just need the code and an internet connection.
If your car is running "very roughly" then I probably would not drive it until I determined the cause of the CEL.

B. One year old gas is not necessarily "bad" gas. As a matter of fact....if it's been hanging around in your car's fuel tank for a year then you probably did more harm with the potions and snake oil than you did by leaving the gas in the tank for over a year. See my avatar? Believe me.....I've SEEN many cars left for a year at a time with gas in the tank for over a year.
One last thing. NEVER buy high octane gas, unless you have a car whose manufacturer specifically recommends it.
No.
It will not usually harm the car, but 99.9999999999999 percent of the people who buy mid grade and high octane fuel are just throwing money away.
I have family and friends in the petrol biz, and they THANK you for the extra money, but...really.
They don't NEED it, and according to your avatar info you live in California so you already pay too much for gas.

III. The easiest way to pump the fuel out of your tank is to disconnect the fuel line in the engine compartment and use the fuel pump.
Your fuel pump runs on electricity, so it does not care how old your gas is, and I'm guessing that you did not put enough snake oil in your tank to hurt the pump - BUT....I'm going to presume for the sake of this discussion that the easiest method for YOU would be to remove the back seat to access the tank top and take the fuel pump out of the tank....and then siphon as much of the fuel out of the tank as you can and then replace it with regular unleaded fuel.
Again....I think that there's a 99.44 percent chance that you're amputating a foot because of an ingrown toenail - but it's your car and your call.

001. According to the info on your avatar you have a G2 Prius, so there's a bladder to deal with, or so I'm told.
There is a sub-forum that deals with that generation that's labeled something like "Gen 2 Prius something or other"
No.
I'm not being a Deputy Bernard "Barney" Fife.
NOBODY likes forum sherrifs, and I'm already a smart aleck BUT I'm guessing that somebody hanging out in a G2 sub-forum will know more about YOUR Gen2 fuel tank.

You can get a forum moderator to move it for you if you wish.

Good Luck!

 

Personally, I really doubt one year old gas could be considered bad. I've fired up vehicles with gas 2-3x that old. In summer of 2008, I even fired up a 1972 Torino that had been sitting 7 years. Just needed some starter fluid(and a battery). It wouldn't idle due to other issues, but that puppy fired up and ran if you kept giving it some throttle..

 

Me too.
I "know a guy" who had a 1970 Chevelle in the late 80's that sat in a friend's apartment complex parking lot for 3 years with a half a tank of fuel (first 4 sub patrols plus a few outings on a skimmer.)
"He" had to move the car from South Carolina to Indiana in a day and so he bought a battery and used a double shot of Bacardi 151 (don't ask!) to get the car started and drove 600 miles non-stop thereafter.

I've also personally seen a sailor park their ride in a parking lot with the windows cracked, walk aboard a submarine for what they thought was a normal day's work only to return to the car 8 months later after the boat was called out suddenly to do "something or other."
That particular car suffered no drive-train issues, but the coastal sun, rain, and salt air didn't do it any favors.
We did break into the car and roll the windows up for him.
That particular sailor was transferred to the west coast (Caly) driving that same car for several years thereafter.

Cars just aren't that fragile, and fuel tanks (rust-free plastic) and other fuel components (stainLESS and/or plastic, and SEALED) have only gotten BETTER over the years, NOT worse.
Fuel is filtered more, stored in sealed tanks with leak monitors, and pumped with better gear than it was just 20 years ago....because DOT.GOV says it has to be.

YMMV

 

Time was, it would sit there in the float bowl of a carburetor, and evaporate, leaving a layer of glop behind. That was not at all conducive to good starting or running. I know a guy that happened to.