Depending on the size of the drain pipe you will likely not have enough room to add a siphon break inside the box so I suggest you drill through the overflow box as low as you can (to allow rim of bulkhead to fit inside) on the left or right. Then install it with just the bulkhead hiding it to the tank (remove the rubber gasket and silicone the bulkhead in, this lasts forever whereas the rubber can erode). Then add a 90 elbow facing sideways with a strainer inside the overflow. On the outside you can put a siphon break to remove any air from the pipe, this would simply be a T with one end facing up, and the other draining to your sump. With the up section of the T add some pipe so it is above the maximum water level of your tank (if you don't want it visible, you can cut it flush with the top of the tanks rim). Then place an end cap with a small drilled hole over it to silence it (not necessary but does reduce noise).
Hard to explain without a pic but if you look at my 55 build thread you will see pics of mine, same principal.
Also make the drain pipe as big a diameter as possible but be aware that strainers are hard to find for 1/4" sizes.
Are you drilling the acrylic yourself? It's very easy, just use a hole-saw attachment on your drill for wood and drill it vertically while someone sprays it with water to cool it.
