I needed to add an exhaust vent to my workshop that would allow me to quickly attach and detach a 4″ exhaust hose. I decided to use an inexpensive   ($3.18) PVC 4″ snap in drain to go through the board I had in my window for the portable AC unit.   The nice thing about these 4″ snap in drains is that they will tightly fit inside of a 4″ hole, or a 4″ exhaust hose.

Plus, I already had the 4″ hole saw from using the same hardware to vent my truck’s battery chargers.

One hole and a bit of epoxy later, I had a way to vent a 4″ hose out my window.

The drain has a large plastic “grid” to keep out larger creatures, and in this particular application, I have the board mounted inside the normal window screen, so I don’t have to worry too much about bugs.   I also purchased a 90 degree aluminum elbow for $4.28 which makes it very easy for me to plug the flexible dryer hose over the plastic drain piece, and makes the 90 degree turn to go out the window.

It currently sits over the plastic with a friction fit just fine, although I may buy another spring clip to make the connection a bit tighter.   NOTE: This 90 degree elbow is “adjustable” in that you can rotate the different sections around to change the amount of bending. Unfortunately, this let some smoke smell escape into the room from the elbow until I covered all of the seams with aluminum foil duct tape.

Because I only leave the hose attached while venting, I also needed a way to plug the hole when I wasn’t using it. Again, the plumbing section provided the perfect fit with this 4″ PVC DWV to Sewer and Drain Bushing ($2.48), which fits over the outside of the snap in drain very tightly.

I cut a circle of 3/4″ poly iso insulation I had left over from insulating my garage doors to seal the inside of the bushing, and affixed it with hot glue.

Now, whenever I’m not using the Exhaust vent port, I just slip the bushing over the snap in drain and it blocks drafts and provides more insulation value than the plywood board I have mounted in my window for the AC unit in the first place.

My total cost for this solution was under $10 (assuming you have 2 part epoxy and poly-iso insulation just laying around…).