Custom Auto Topoff with Fail Safe for you sump
 

This unit has two floats, one for makeup water and the other float for high level cutoff. You hook this directly to your RO, no need for pump or any else.
This unit cost me $300 asking $100 used for 3 years and never had problem.( This is used in your sump )

http://i840.photobucket.com/albums/z...1/IMG_2503.jpg