I have an different opinion than Melev on the drilled holes. Drilled holes, just like check valves are a false sense of security and often fail when you need them most. The best form of backflow prevention known to man is a simple air gap. By this I mean place the Loc Line nozzles only that 1/2" or whatever below the normal operating level of the display so when the power goes off or the return pump is shut of, only that 1/2" or any other very easily calculated amount of water flows back to the sump before the siphon breaks when the return nozzles are exposed to atmosphere, an air gap. We all know water cannot jump uphill so it cannot be defeated, requires no cleaning or maintanance and you can sleep soundly at night whithout worries of a flood. Drilled holes plug with algae and get dirty or a snail parks over the hole, or when it is needed a small fish or anemone gets sucked up against it, or some floating foozen food etc. Same with check valves, it does not have to be a catastrophic leak, even a grain of sand will defeat a check valve and flood the sump before you get home and notice it. And what is to say you cleaned the holes last night and today there is a power outage and your anemone just happens to be next to the hole and gets sucked up? It can happen at any time no matter how much maintenance you do or don't do as the case may be. They fail.
If we use my display as an example, it is a 60" long 100G that is 18" front to back and my Loc Line returns are 3/4" below the surface. That equates to 3.5 gallons that flows back to the sump in a power outage before the air gap is created when the returns are exposed to atmosphere and the siphon breaks. To calculate the gallons that could potentially backflow it is L x H x however many inches depth divided by 231, in my case 3/4" or 0.75". So 60 x 18 x .75 = 810, 810/231= 3.5 gallons.
Since my sump is a 30G and I run it just less than 2/3 full since this is where the skimmer operates most efficiently I always have 10+ gallons of freeboard or spare room in it at all times so a flood isn't going to happen. This particular system is almost 11 years old now and never had any issues. You don't need holes as long as you amke sure you have sufficient room in your sump to contain whatever backflow you feel comfortable with. I could drop my Loc Lines to close to 2.5" deep and still contain any backflow which is a good cushion.
