Dank_Solo

A dry vent has to be installed vertically from the trunk line because if waste ever backed up into a horizontal section of dedicated vent pipe that you couldn't run water through it would dry up and plug the vent. A "wet" section of vent can be horizontal because it can be rinsed/accessed (other than the roof!) Wet vent systems and dry vent systems have different applications. For example, we try to pipe all of our bathrooms in a way that the lavatory's stack vent is close enough to serve the tub and water closet. We can't all the time though (mostly in super huge master bathrooms) so sometimes we have to add a dry vent to serve the fixture that is too far away (almost always a shower or garden tub or both). This leaves a vertical section of vent pipe only accessible through the roof. Hopefully all of this information is still technically correct. Just thought i'd add a little practical info on how/when they are used in a home. Commercial buildings use almost exclusively dry vents, but those systems are engineered, residential plumbers have to figure the drain layout for themselves, as they are only given a floorplan, not a plumbing diagram to follow as close as possible. Greetings from Augusta, GA. Go Dawgs!