MudRunner

Go to multiplayer and load up the map 'Island' on Casual using the default vehicles with a friend and have both players attach the Trailer hitch and Utility Semitrailer to the rear of the 'B-131' or 'C-255' truck. Next you are going to want to navigate your way down to the Fuel Station towards the SE corner of the map. Once both vehicles are here, have each person fill up their Utility Semitrailers with fuel. The person who is not going for the achievement first will need to apply the park brake to their vehicle and ensure that 'All wheels' is off and then simply just hold the acceleration down which will have the fuel consumption immediately deplete by 1 litre. At this point, the player who is going for the achievement will need to select the semitrailer to fill up the other vehicle and continuously spam the button which will result in it refueling the vehicle by 1 litre each time you press it. Using this method will net you the achievement in just a couple of minutes.