Drilling anti-siphon holes

[newty]

Hello,
I have completed the overflow (U-tube) slash return system. I want to drill anti-siphon holes in my return pipes (I have the return split into 2 pipes). Anyways, where do I drill the holes and how big do you recommend them to be? Do I drill the holes where the pipes are submerged in the water or in the part that are not submerged?
Basic info:
Pump: Mag 9.5
Split return pipes: one 1" pipe into 2 3/4" pipes.
Returns are ~2-3" deep into the water
Thanks in advance, Shawn

 

[1911_guy]

You drill the hole just below the water surface where your return line goes into your display tank. Make sure the hole is not facing up or your return water will be pumped up towards your lights. I think most people drill 1/4 inch as a siphon hole.