Why won't my fuel gauge stack?

[PandoraIV]

When I did my assembly of my spacecraft all of the parts went on just fine. The problem is that the game isn't recognizing that I want the stacked fuel tanks to go into that specific engine and is only letting me use one of the fuel tanks. What is the problem and how do I fix this?

[relicen]

Do you have a decoupler between the tanks? Decouplers don't transfer fuel, so tanks that are meant to feed between each other should not be separated by decouplers.

If that doesn't solve the problem you should post a picture of your rocket. It would make it easier to figure out what's wrong.

[stupid_chris]

The tanks drain one at a time starting from the top most first, so if what you're trying to say is that only one tank is draining, that's normal.