Sewer stink

We were just away from our rv for 12 days and had some amount of waste in both waste tanks when we left. We ran water into the drains and then used the drain plugs/baskets to close each drain including the shower. Water in toilet bowl and lid closed. We did not have any odor when we got back. I would guess that one of the air admittance valves is not working property. They are cheap and easy to replace - can't be purchased at Menards, Lowe's, or usually any store that carries plumbing supplies.