JSB99

No updates from you in a while, hope everything is alright...

Thank you sharing your project with us. Take care.

Groovin'

So, the solution to your issue is to draw a vacuum on the tank that you are trying to fill before you start trying to fill it. The problem is that you need to remove the air from the tank before you can fill it, as air does have a volume. Without "creating space" by removing the air first, your tank won't fill, and instead will just overflow out the bottom of anything that might be gravity fed.

The solution is discussed in detail here:
http://forums.adafruit.com/viewtopic.php?f=8&t=49627&p=250085