Originally Posted by Caocao
A normal drainage slope will not affect how much gas you can put in your car.
There are a variety of factors that determine how much gas you put in your tank when you fill up. Slope, speed of the fill, topping off, etc. For example if your tank is 2' long, 1.5' wide and 8" deep and you are on a 2% ("normal" by the way) longitudinal slope with the tube going into the tank from the end the difference in filling up facing one way vs. facing the other is about a gallon. If you have a Scangauge or similar it's pretty obvious. The capacity of that tank would be 15 gallons, by the way. That's why after about 5 fill-ups I only adjust my Scangauge one tenth of a gallon at a time. It's also why quoting the "last fill up gallons " vs. miles is not very accurate, although if you're hunting for good news you get it about half the time.