Okay here is what I came up with after several attempts and a few leaky ones from being in a hurry.
I still used 3/8 inch O.D. tube and made the bend tight enough so that I don't need any suction cups at all. the Drop checker just hangs on the tank and stays in place. While the bend was still hot and a little workable I pushed it down on the tank edge so that it would sit really well.
Behind the color indicator solution I just put a small piece of white peel and stick label. White vinyl tape would work good also. The bottom two images show when it was first put into the tank (blue indicator solution) and about 2 hours later (green indicator solution). Seems to be working just fine.
Thank again for the idea Brohawk