We are building an earth sheltered house in Newport Oregon. All the drain lines are set into the slab and we have a vent pipe going up through the shell of the house (then 3' of earth) and out. We set that pipe inline with the tub, and toilet drain but the Vanity is on the other side of the bathroom. There is no easy way to tie into the vent. (no attic space) and I was wondering about the use of (I think they call it) a Pop Vent. This would then be inside the wall with I'm guessing some kind of access panel. Any thoughts? It won't be impossible to get the vent line over to the other line but it would be quite a circuitous route.