I just use a cheap gravel vac that doesn't even attatch to the sink. It has a hose about 5 feet long, about 1/2 inch diameter inside. The attatchment for the gravel is bigger, maybe about 2" wide. I stick the end of the hose in a bucket, at least 2 feet below surface of the water. (the lower the end of the hose is relative to your tank water level, the more the suction will be). I stick in the gravel vac end (into the tank), and let that fill up with water. Then, I point the open end up a bit, and raise it a few inches above water level. Keep the vacume end pointed up! As soon as water is going down the hose, lower the vacume attatchment back into the water, still pointing it up a bit. (when I say pointing up, doesnt have to be straight up, just slanting up) Water should still be going down the hose into the bucket, and now the vacume attatchment is under water. As long as you time it right, the vacume attatment will fill back up with water before all the water goes down the hose. Now, the vacume is under water, it is filled with water again, and water is going down the hose into the bucket. Now you can point the vacume down to the gravel, and get the job done!
The only tricky parts are:
1. keeping the vacume attatchment slanting up until you're done getting it started
2. getting the time right - raise the vacume attatchment above water level, lower it back into the water AS SOON AS WATER STARTS GOING DOWN THE HOSE, while still slanting the vacume attatchment up
Maybe I'll take pics next time and post a step by step tutorial, since there seems to be a ton of threads with using gravel vacs, especially with getting the syphon started. Who know, it could be my first sticky then!