Ditto, it's critical that the tool engages the three "teeth" back inside the female connection end. Be sure the connection does move a decent amount without the tool in place, because the tool has to be inserted far enough to push all three tangs outward enough to miss the tube "lip" that locks it on.
If the parts are pulled apart too much while the tangs don't "let go", the tangs will get bent some, and that makes it super difficult to get them to release.
I had that issue with mine on my 98 Mountaineer. In about 2005 I had a non starting issue that I went at the pump to fix, and discovered that the flexible SS line was damaged near the tank connection. Someone previous had been seriously pulling and twisting, yanking on the line to get it off. I was stunned to see that damage to a SS line you would think of as robust and strong. But it hadn't leaked and I was careful in removing the line. It was very tedious and I got it cleaned well and looked at it closely with a mirror. It took a while, but with it finally off I saw two of the tangs bent sideways some.
Be careful with those connections, the fuel filter connections are also the same way. I fixed mine the next time(2014) by buying a spare fuel line from the tank to the filter, and replaced the old one.
