Make sure you are comfortable with going to the bathroom in the great outdoors!
Do some camping prior to the trip. Make sure you are comfortable with going to the bathroom in the great outdoors!  More and more there are toilets dotted along the trail, especially lower down.  However, not everywhere.  Sometimes, you will have to go to the bathroom when on the trail and there will be no toilet in sight.  Being comfortable with some of these things will make the entire process much easier when you arrive in Nepal.