Because boiling removes oxygen from the wort, it must be added back so the yeast can have a little clean air along with their grain. You can attach a hose or tube that reaches from the kettle to the bottom valve (or racking port). Again, using a closed system, add a T-Fitting to connect oxygen connected to the T-Fitting. Transfer at 2psi into the hose used to transfer the wort from the kettle. The oxygen will mix with the wort as it moves from the oxygen input point to the fermenter. This is why you need fix or six feet o tubing. This method is simple and means you do not need to add an air diffusion stone in the fermenter, which could be another source of contamination. We may add this to the Shop soon! There have been a lot of requests.