You'll need to provide yourself access to the water reservoir under the egg crate. You can do that a few ways, drilling the lower portion of the side of the tank and installing a bulkhead, or just silicone in a "vent tube" in a corner of the tank. The pipe should start below the egg crate and end somewhere near the top of the tank. Remember to cover it in some way to keep "food items" from crawling into it. Then run a length of airline down the pipe and into the water. The airline should be long enough that the end should hang .lower than your water line. Put a check valve and a gang valve at the end of the hose. Start your siphon then close the valve. Now anytime you need to drain water, just open the valve