Where to locate vented loop in the system?

[CNulli]

Hi, I am adding a pump out for the head. I have a tank, through hull for output, a vent for the tank, and of course the head. I am adding a valve to select pump out or overboard and a vented loop. I have two designs and would like feedback. The first, A, has the vented loop between the valve and the through hull. Option B has the vented loop between the toilet and the group of valve, tank, and through hull. The tank has a vent that is always open. At first I thought option A would be best, now I am considering option B as it would alleviate back pressure on the toilet from the holding tank. Your thoughts will be appreciated! Thanks

[GordMay]

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