Hi folks. I need to install an Air Admittance Valve for my kitchen sink. I have seen more than a few pictures of these installed under sinks (many of which look like they're done wrong.) My question specifically pertains to where the vent should go. In some pictures, I see the vent installed at the top of a drain that goes straight down, vertically into a wall or floor. In others, I see the vent installed with a sanitary tee on a horizontal pipe that then connects to a pipe that goes downward (see pictures.) Are both these methods acceptable? For some reason, I feel that a vent installed at the top of a downward vertical pipe is best.
AAV installed atop a horizontal pipe
AAV installed atop a vertical pipe
AAV installed atop a horizontal pipe
AAV installed atop a vertical pipe