Mike
there was a lot messages regarding this issue,,( a whole lot during the summer),, I for one just monitor and estimate how much water I'm going to need to in regards to filling the tank,,,I normally try to keep the tank as low as possible just so I do not carry the weight around. If you look at some of the pics of the rear tanks not an easy place to access,,, also as far setting up a drain don't forget it's going to have to be lower than the tank to drain,, I drain mind at home with a bucket so as not to waste the water,,,, personally a lot of work for a project,,, if how ever you do do it,,, take pics I could change my mind and do the same haha
sparky