my bongs and vape don't get stuff in my mouth except for thc. Have you tried putting water in your bong? that will keep ash out of your mouth
things you cant see/taste/feel, tke a look at your piece and all the particles stuck to the inside of it and tell me none of them are making it into ur mouth hahaha.
btw if all you get is thc you must not be smokin marijuana, friend.