My truck came with a 3/4" tube hanging down on the drivers side at the rear of the oil pan. I bought enough 3/4" tubing to snake it through the frame and have it poke out just about at the end of the cab, then I used a 90° tubing connector and added about a 15" piece so it shoots straight down. This really keeps the underside of the truck clean, and you don't even see the breather tube except where it exits the frame rail. I would not down size the vent, and instead run the same or larger size tubing.