I made one of these drop checkers out of 3/8 inch O.D. tubing and set it up in a tank with an in tank drop checker. Took a couple hours but it is working great! I was wondering if being external to the tank would make any difference. I've got one other idea that I want to try and then I'll put a few images up.
Great idea Brohawk! So cheap and no big suction cup in the tank.