Definately need a anti-siphon hole. On the sump side, the hose is above water. I have the anti-siphon hole right above the pump in the top off water container. I make sure I never fill above that hole.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,