The gray and black water holding tanks need ventilation to the roof but i see nothing in nfpa 1192 indicating that both tanks can t share a common vent.
Waste holding tank vent.
Airforce filters holding tank vent filter new installation kit 1 1 2 hose size 5 0 out of 5 stars 1 alpha pure boat marine holding tank vent filter with 5 8 3 4 1 1 5 adaptors mhtv 100.
The 360 siphon rv holding tank vent cap eliminates odors from the source the holding tanks and exhausts them out the roof vent before they have a chance to invade the rv living space.
Every holding tank needs to have some manner of ventilation.
With no outlet for escape the noxious tank fumes seep.
By design the patented 360 siphon can only create an updraft expelling odors and fostering an oxygen rich environment to speed up waste breakdown.
Remember the aerobic bacteria which digest waste and don t produce odor in the process require oxygen.
The solution to holding tank odor either inside the tank or in gases leaving the vent involves better ventilation specifically cross ventilation.
From technical editor chris dougherty.
Eliminate boat holding tank odors using big orange waste holding tank vent filter.
No treatment chemicals needed automatic bypass valve reduces tank collapse.
Unexpected sewage odors that appear in the bathroom area of your rv can indicate a clog in the air vent leading from the black water holding tank to the roof.