All aircraft have a supply of map cleaning fluid , all you have to do is slightly undo the screw at the back of that thingy in the centre of the windscreen with the numbers and letters that wander around on the face and it will despence a small amount of map cleaning fluid. The fluid dispenser is much better positioned on the Cessna (rather than the piper ) as it has a convenient shelf to let you position the map exactly underneath the fluid dispenser.