There are 2 or 3 buslines bus lines going from Amstel station (152, 157 and ?). Step out P&R Muiden, walk under the highwaymotorway-bridge, walk ON the highwaymotorway, over the river, 300m in the direction of Germany and you'll get to the petrol station.
If you go towards [[Hannover]], [[Magdeburg]] or Berlin, be aware that the first petrol station in Germany is '''after''' [[Osnabrück]].