I have seen several posts where people have their blowoff tube get clogged when using the 3 piece airlock and 1/2 inch tube. As seen in the picture my airlocks had extra material at the bottom that would easily clog up when krausen got into it and you end up with the mess you were hoping to avoid. I simply cut away that plastic and cleaned up the end with an exacto knife and now have a nice opening for everything to flow through.
Happy Brewing
Happy Brewing