So I've put together a really simple carbon filter/scrubber design for any 120mm fan. My inspiration was this DIY filter only I wanted to buy even fewer parts, and have it more streamlined (none of that aluminum mesh/end cap stuff). So here goes: 1. Any 120mm fan will do, but I spent a little extra change and bought a Scythe Slip Stream 110CFM fan (not including cost because you should have fans anyway!) 2. You will need to buy a 4 inch duct connecor. Looks like this, but it's 4 inches. Cost: $6 3. Duct tape. Cost: $5 4. Honeywell universal replacement carbon filter. Cost: $12 5. Dryer vent pest guard. Cost: $5 Total cost: $28. I found everything except the fan at Home Depot. It's dead simple to put together. The dryer vent pest guard is exactly the size of the rectangular part of the duct connector, so you cut some strips of the carbon filter and line the inside of the pest guard, tape this to the duct connector, and attach the fan to the circular part. Simple, and I even have enough left over to replace my carbon 2-3 more times if I need to.