i have an older house where the kitchen sink is not properly vented. it's a double-sink on the first floor and the plumbling runs into the basement. the problem is about 10' on the horizontal drain, there is a 'vent' that only sticks up only 4' or so and is open at the top. water comes out of it when i have a full sink and let the water out. the plumbing in the basement runs about 25' along the wall and makes a right turn (along the other wall) for about 10' and then into the sewer line. it is not pitched properly (no way to avoid it) would an aav valve be a good idea under the sink? any suggestions?