I posted about this before in my discussions of my garbage disposal installation, but I wanted a fresh thread in case stuff got missed. The old configuration was a mess (the garbage disposal did not drain well): Because it was already S-trapped and there was no available outlet through the wall for a vent (and I needed to get this fixed asap since the sink had been out of commission and dishes were piled up), I temporarily used this setup: I then started thinking of how to configure it so that I could get it vented properly (AAVs are NOT allowed in my state so that option was out). I came up with this crappy rough sketch. After looking up some parts I started to get a better idea of what I could do. I figured I could use a compression to PVC fitting to bridge it to a 1 1/2" sanitary tee that takes it down to 1 1/2" to 3" (or 2" if it turns out that is the pipe size under the house) wye to hook up to the existing pipe that has a cleanout and on top of the tee I would have an elbow to take the pipe out through the wall at an angle (so it would not be a flat vent) and another elbow to make it go up outside the exterior of the wall. (obviously that is not to scale) Then my next hurdle is the window above the sink. As you can see in this photo, the existing vent pipe routes around the window. I'm not sure if it is actually 6 inches above the flood level and this terminates under the soffit. So, once outside the house I would need to route it around without having it go flat/horizontal before the 6" mark. I'm thinking another elbow or something and trying to get it to start going sideways at an earlier point with another elbow. I'm just not sure how to measure for the angles and where all of the holes should be. I am not thrilled with drilling through the siding, but I don't want to tear up the backsplash above the sink. (I don't care about the look under the sink). Is the configuration in my last sketch OK? Should I make any changes? Any advice? (I know Chris mentioned Sika Flex as a sealant...) I admit that while I know the rules on the required slope, I am not exactly sure how to check the slope when I'm dealing with stuff that isn't square/level. Any tips on how to do that? Is there a set angle for particular slopes? (this sort of thing was not covered in my college math classes years ago).