I would like to see an IPC image or Maintenance Manual reference.
"If" your aircraft have a vacuum lavatory system, there is a large tank (usually) located back near the aft pressure bulkhead. This tank will have a suction pump located on it. Tubing from each lav is connected to the tank. When a toilet is flushed, a blade valve will open on the bottom of the toilet. At the same time the vacuum pump will turn on. This should draw any contents into the tubing leading to the tank.
I'm not sure what Boeing calls the "breaker valve" in this system. My guess would be the blade valve, but an image should provide the answer.