If the Liquid level in the Digester raises above the Outlet pipe, it will discharge as rich liquid Fertiliser to wherever you plumb it too.

Some customers simply discharge the liquid Fertiliser into an old Septic System & let it Leach out naturally.

If Digester is left unused for a long time, and the Liquid level drops below the Sink Inlet level, Air will enter the Digester, then you will have to re-start the digestion process again.

That should Not happen unless the Digester is Not used for a very long time or you get a leak in the Plumbing or Digester Bag.