Both good ideas, i just hit up my local vape shop today, i got a mouthful of grinder dust yesterday and it was nasty. Lol. He gave me a bag full of the tester tips, i only wanted a few for letting people Att work try my setup out, but putting something like silicone in the hole may just be the best answer at this point. Bottle nipples would work too, but I would think would be considerably large unless you really cut them down and which then they will probably fall off too easy, but I will say interesting idea. I have designed a drip tip with a hinged stainless cap in my mind, but have no idea how I could bring it to fruition. The trick would be getting the hinge to drop back low enough to not hinder the hit. I think it would require a double hinge setup with a little arm to kick the cap away from the tip a little. I think if someone could make that with a clamp on it for attaching it to your favorite drip tip it would sell really well. And yes I have out considerable thought into it. Particularly for vapors with dirty jobs it would be a lifesaver.