I would place a filter (such as a K&N) onto the end of the draft tube.
What would it filter you ask? What do you suppose the piece of chore boy stuffed in the end of the draft tube filters? The purpose is to keep dirt and debris from entering the tube, which is inturn a direct connection to the inside of the engine case where your pistons, rods, valves, etc. reside.
The air movement in the draft tube will move in both directions (in and out). The pressure inside the engine case changes from above atmospheric pressure to below atmospheric pressure. If it didn't, you wouldn't need a draft tube.
It would help just to attach a long heater hose to the end of the draft tube and run it to the rear of the vehicle, making it less possible for dirt and debris to reach the internal engine.
