I never have to wipe my funnels because I have different ones for different fluids - oil (engine oil, ATF, power steering fluid), coolant and brake fluid, and I store the funnels in clean plastic bags, inside an enclosed cabinet. The bags get changed after a few uses.
For WWF I use a screw on spout and leave the spout on the jug. I slip a cap over the spout to keep dust out.