So I got a gas can like this. Now my question is the small yellow cap at the back. Is that supposed to be on tight so it seals. So if I blow in the front no air should be escaping from the back cap? Is that just a hole to open when you pour gas so it doesn’t glug glug? I thought that was the point of the special self venting spout…
It’s called a vent cap.
You open it when you pour gas out of the can.
Tester
You’d think that self-venting design for the spout would eliminate the need for another vent. But it appears from the photo the self venting design is geared more for lower flow rate pouring; if you were trying to pour gas as fast as possible the space around the outlet might all get filled with liquid gasoline and the self-venting spout idea wouldn’t work.
You can buy those little plastic caps on ebay. I have added them to all my plastic cas cans because all the self venting spouts don’t work wort a hoot. You just drill a 1/2 " hole with a spade bit and pop them in.
You use the self-venting nozzle when filling things like lawn mowers, snow throwers, etc…
But if you use the gas can to add gas to a modern vehicle gas tank, the ORVR system won’t allow the gas can to vent properly. So you open the vent cap.
It’s an EPA thing.
Tester
Ok thanks guys 
So keep it shut tight when it’s in storage so no water get in the ethanol mix?
Always add a fuel stabilizer such as Sta-Bil when storing gasoline.
Tester
It’s only going to maximum 1 month maybe. It’s E85 so it’s even less store able right?
Would you recommend it’s for 1 month?
What do you have that can use E85 . I know your BMW can’t . I certainly would not put it in lawnmower.
Soooo?
Are you planning to use that E85 gas in a flex-fuel vehicle?
Tester
It’s to run E fuel mix maps on my car.
E85 is rare in Canada. This “local” sports club 40 mins away sell some. I only plan to use it at drag days at my local track so having a 20 litre few weeks before for when I go will give me a full tank of E30 mix when mixed properly.
Yes it can.
Alcohol drag racing?
You’re good to go.
The gas can will work.
Tester
Alcohol lasts a mighty long time.
Yeah but I’ve been told E85 has a tedency to absob water, kinda like brake fluid.
So the container has to be saeled really really well.