I would suck it out also or stick a small powerhead/return from a filter reactor in the area that gets the build up. I have this problem in certain spots but only clean it when I service the pump.
Not all tanks have tempered bottoms. I have actually seen many that don't. I just put 2 holes in the bottom of a 40b last summer. You could drill the bottom if the manufacturer clarifies if it is tempered or not. I think you should just drill the side and put in a small overflow box like Bryan is talking about. That's what I would do with or without a tempered bottom. Just my 2cents.
I would just use epoxy to seal up the foam and then stick sand to it for texture. Make sure you get all the foam sealed up because it will break down eventually from your lights.
Cool! It's great to see a new reefer in Eugene. Welcome to the area! That is an interesting idea on your return. I like people experimenting with new ideas on their tanks. It keeps things interesting. I agree with drilling your tank also. It's super easy and much more effective. I would go with an overflow box because your water skimming capabilities are greatly improved. The one newfisher has should work great if it's the one I am thinking of. If you need it drilled I know several of us around here have bits. I have 3/4" all the way up to 2" glass bits depending on what you would like to do. Good luck and if you have any questions or need someone to help shoot me a pm.