Okay, to start things off, I hate hate hate using silicone in my tank because I just don't like waiting for things. I also needed a drop checker so I made this. I made this out of stuff every aquarist will have:
1x 3 inches of PVC
hose, the same diameter as the stuff on your Python
1x 1 API water test get vial
1x 3 inches of airline hosing, the really thin kind (make sure it is clear)
1x piece of plastic to plug up the airline hosing (I used a air control valve with it screwed in all the way so it becomes air [and water] tight)
1x Suction cup with a nipple
1x suction cup with a clip
And a small amount of Drop checker solution which you can find a formula for on this site.
This build takes about 10 minutes cost should mostly be ~2$ if you don't have any suction cups.
1. Take your pvc
hose and using a sharp pair of scissors cut an "x" or "+" into it about the same diameter as your suction cup nipple. Do this about 1 inch away from any one end of the pvc
hose. Insert your suction cup
2. Insert your API test vial, bottom first, into the pvc
tube 2 inches in.
3. Take your small piece of airline tubing and plug it up with whatever you have on hand.
4. Attach a suction cup w/ clip to the airline tube (you can get em at petsmart for about 1 dollar a pack) to the tube.
5. Fill the airline tubing with with your check solution. (you're using a tiny amount, this is a tiny unit)
Now comes the tricky part
6. Place your API tube set up over the airline tubing holding your test solution and lower the whole apparatus into the tank, making sure to keep it as level as possible to keep water from getting in.
Voila you're all done here is a pic without the test solution: Although it's not pretty it will get the job done and its slim nature makes it an easy hide behind a filter tube.
UPDATE: Picture with test solution, you can't tell but the fluid went from a cobalt blue to being a light greenish-blue in a few hours.
Another update: It seems that this drop checker is extremely sensitive to changes. I upped the CO2
on my tank and in a few minutes the green turned another shade, well, greener. Most likely because there is such a small amount of check solution, gasses diffuse in and out of it faster.