Why are you guys using your mouth to start the siphon? They surely should be putting instructions on these thing as no one, even me in the beginning had any idea how to do it and I used my mouth too. The trick is to make sure the siphon is full of water first. I normally just scoop as much water as I can with the wide part of the siphon, then turn it vertically so it starts flowing towards the bottom. You have to use your finger at the bottom to stop all the water from flowing out of it because the purpose is to fill it up with water to the top as much as possible. Then once full(as long as the airline is full), put the wide siphon part back in the tank and reIease your finger from the bottom to let it flow. In the beginning it may take you a couple of water scooping, releasing your finger at the bottom to clear all air bubbles along the way but once you grasp it it takes a second from the first time.
I just couldn't get the hang of that at all. I use the suck method, and keep my eyes fixed on the tube to see when the water is about to reach my lips.