Oxygen free dry hopping

Trick 1
If you have to open the lid for whatever reason (e.g. dry hopping / hop spider) and you don't like the idea of fresh air in your keg, you can purge oxygen out with CO2.

Simply connect your CO2 as usual to the closed lid, let some CO2 flow into the keg, wait a couple of seconds and use the pressure valve to release oxygen (which gets pushed up) from the keg. Pull up the pressure valve for a second or so.

Repeat this procedure (add CO2 > wait > release pressure) three or four times for a full keg and your oxygen should more or less be gone.

Trick 2
You can also use the trub container to avoid oxidation during dry hopping. Here's how it works:
 * Close the valve, remove the trub container and clean/sanitize it
 * Fill the trub container with the hops
 * Purge the container with CO2, attach it to the keg and open the valve
 * The dry hops will float up into the keg automagically!