Auxiliary tank gas-transfer puzzle 73 GMC

[MusicMan70]

Because of the known venting issues on the standard tank and slow-filling/burping at the gas pump, I figured I'd just use the Auxiliary until I remedy the problem on the standard tank(aux tank fills quite easliy as it should, unlike the factory unit).

The main/standard tank had about 1/4 tank of gas left in it per the gauge. I filled up the Aux tank and noted 20 gallons at the pump(I had never filled it up before). Flipped the toggle under the dash and it began to move and read full plus.

So I'm driving home from work next day and noticed my gas gauge needle had dropped to about an 1/8th...Hmnnn. I check my toggle to make sure I didn't flip it on accident; I hadn't. Once home, I flipped the toggle over to the Main/Standard tank and it read Full+..?! But how the....anyways

I shut off the truck and when I get out to inspect , I immediately smell gas. Look under to see gas dripping from the passenger-side area of truck. I go to remove the gas cap on the Pass/main tank side and it starts to spurt out. I remove the cap on the Aux/driver-side, thinking that may help relieve some pressure; nope still spurting main side.

I get a bucket and take the main tank cap off and it spurts and pours out gasoline. I siphoned out about 5 gallons and that cured my spurting-gas dripping issue.

1- I looked under the truck and the valve switch unit was not leaking
2- Aux gas cap says "VACUUM PRESSURE" Main cap says "Anti-surge" inside
and they both "whoosh" when I remove the caps(when they have some gas)


Q1-Is this Valve system designed to keep the main tank full or should they operate as separate fuel tank units?
Q2-Does this mean I need to replace the valve or caps or both?

Here are some pics and thanks in advance for any guidance