After testing the tank again, I found that one of the screws on the cover plate was leaking. Since I needed to do something about those screws, I decided to fix the flop tube. When I originally installed this 90 degree bulkhead fitting, I didn't get it tight enough. So when I installed the cap, the flop tube turned somewhat.

After going to Sears Hardware to get a crow's foot wrench which I could use to hold the bulkead fitting from spinning while I tightened the nut, I removed the fitting, replaced it with a new one, cleaned everything up, reinstalled the fitting (tightly this time) and sealed over everything again.

Here you can see that with the fitting in the correct orientation, the flop tube points directly aft and not towards the top or bottom corner (as before).