As I've stated before, the exhaust features of the K40 are laughable at best. A very poorly constructed "squirrel cage" style bathroom fan slides into some brackets on the back of the housing.
Here is a picture of the unit off the machine. It probably moves all of 30 cfm (Cubic feet per minute).
This is my upgrade, a 6' inline fan, designed most likely for agricultural applications such as venting green houses. It moves around 300 cfm and cost around $56 on Amazon shipped. I was originally trying to do the exhaust on the cheap, sticking with a 4" diameter fan to keep the size consistent with the plumbing. None seemed to move enough air so I went with the 6" fan. The out feed hose may need to be as long as 12 feet, so I needed to really push some air.
You can see from the pictures that I've had to use a 4" to 6" adapter, and you can see how it attaches to my other adapter at the back of the laser. I've tested it once and it seemed to work pretty well. There were a few leaks in the seams that need to be addressed. Hey, that's why they call it duct tape! I'm still using the super cheap blue exhaust hose that came with the unit. I'll replace that with some dryer ducting or drain tubing soon.