The closest Hess is on WDW property.
When leaving Fort main entrance turn right, come to stop turn right, get in left lane, follow signs to Polynesian, go until road stops and turn left. Hess is on your right. This one has diesel.
To get back, turn right out of Hess and take first road to left, stay on until you get to Fort entrance.
That Hess has always had pretty good prices. I go there to fill up before I get the trailer hooked up. Pretty easy to get there and get back to the fort.
If you are interested in driving into Kiss...the walmart on vineland rd has a murphy gas. You need to use a walmart gift card but you can then get the cash price for gas and it is the cheapest we have ever found. The hess stations are also good as well as the one at the car care center.