Jart, yes that is what I meant regarding the possibility of the aquarium/filter water possibly being able to get into the potable water supply of the home.
People that use automatic drip systems or float valves on a sump system don't have the fresh water entering below the tank or sump water level.
As Hoppy mentioned, you want to prevent backflow from the aquarium/sump to your household water.
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry