Go to RV Sani-Con System
for the service manual. On page 12 there is an exploded view of the parts. The bypass hose is #20. This is what I have. I stay in one place for months at a time. When the black tank gets to 3/4 full, I close the grey valve. When the black tank is full, for me, so is the grey tank. If your SaniCon does not have the grey water bypass there is no "official" way to add it.