Explain dual tank operation

[TrybalRage]

Hey everyone. I have a 1985 C10 with dual tanks, I've owned it for over a year but only ever used the driver's side tank. I verified that the switch worked, seeing that the other tank was empty, and just went back to the driver side tank.

I have a long road trip coming up, so I decided to test out driving with the other side - I put $10 of gas in, flipped the switch over, and it read a fuel level. Drove around like that for a couple of days.

Yesterday I filled up the passenger side, and then flipped the switch to the driver side tank - I was going to leave it full for my trip. The gauge correctly showed (Driver)half full/ (Pass) full when I flipped it back and forth. Kept it on the driver's side, and went home.

This morning, fired up the truck, and the tank immediately read Full. This is the driver's side, that just yesterday was showing half. Flipped the switch to passenger, and it now reads only 3/4 full.

WTF?

Where I park, there is a slight lean towards the drivers side. Is there some kind of crossover tube that balances out the levels? I wasn't aware of one, but I've never really looked or used the tank, so I'm a little puzzled.

Now I'm worried that the fuel level isn't reading correctly, and again with this long trip I'm not thrilled that I'll basically be guessing how much gas I have.

Any insight? Thanks in advance.