A vacuum cleaner. Any model will do.
Straight piece of PVC tube, at least 1 meter long. Longer is better (see the text on tweaking)!
Inner diameter 35 mm (1.4").
A PVC 3-way junction with an angle of 45°, that fits the straight PVC tube.
Duct tape.
A projectile: I used the plastic capsule that is inside "surprise-eggs" (see picture). Old school film containers work as well. Whatever you use, make sure that the projectile's diameter is just a little smaller than the PVC tubes'.
A small piece of cardboard (business cards are perfect).