Hello and Welcome to R2R! I have two holes in each of my overflows with the smaller hole being the return line with the larger one being the return to the sump. The return is solid for most of the way up the water to a flex attachment that can be adjusted to the height of the water in the tank. That way the return helps with the surface agitation. The return has a pipe that has holes in the top with a cap. The cap has one hole in the top which I had to put a small tube into to help stop water noise.