You could drill the 10gal and place it higher than you main tank. Then pump water from the main tank to the 10gal, and it would then overflow back to you main tank. It would cause microbubbles, and you main tank level would fluctuate based on evaporation, so this might not be the best deal. the best way is with an overflow from your main tank. try Lifereef.com if you dont want to drill your tank, they make a flawless hang-on-back overflow that will never loose siphon. It is reletivaly expensive but it is definately worth the piece of mind knowing you wont have 55 gallons of water on your floor when you get home!