The water just comes out the bottom holes. I drilled quite a few. The 3" pipe is about 3-4" above the water line in that section of the sump so water doesn't flow out of the top. It really cut down on the microbubbles coming into the sump from the overflows.
They aren't glued to anything. The 1" pvc
drain line goes down into the 3" pretty far and at a slight angle so holds it in place. I can't take the 3" pieces out unless I take out the 1" piece 1st.