Are you still confused?
Most commonly, a PB "capable" valve has TWO return ports. If not using PB, you can use whatever return is most convenient.
With the PB adapter....it threads into one of the tank ports and supplies down stream valves. The other tank ports is now your standard tank ports.
So without PB, one port is just blocked and one used for tank.
With PB.... BOTH ports are used. One with the PB adapter.
If you try to supply downstream valves with just a tank ports and no PB....you will likely blow the seals that seal the spools to the casting and leak profusely Everytime you use a downstream function. That's best case scenario. Worst case is you can damage, crack, or blow apart the casting.