if u want to be able 2 seee how full it is with out making a float,u can get 2 grommets 2 half inch 45 degree bends and a length of blue see through tubing.drill a hole at the bottom of the rez and one at the top,put your grommets and fittings into your drilled holes and slide the tube onto both 45's its water proof and will show u your rez level,just make your water level indicator on a side thats not in direct light.