Yes, the Bottom is open, except the dark material that you see is 30ppi filter foam=(30 pores per sqaure inch) to keep the bubbles from just being blown out the bottom.
You shouldn't need any glue/silicon. Just drill a hole big enough to squeeze the tubing through.....5/32"-3/16" drill bit should do. Many folks here use 11/64" drill bit, but I don't happen to have one of those. Start with a 5/32" and go up to the next largest if You need to....Cutting the tubing end at an angle will help get it through the hole.
Once You find out what size hole you need: You can drill a second hole and barely put a second piece of tubing in and run it to the venturi hole on the powerhead as in the pic above.
HTH
Last edited by Naja002; 03-01-2006 at 05:23 PM.
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