Or go one better and just use a bbq lpg reg connected to co2 as a cask breather.Saw a Youtube clip hand pulling from a keg whilst the vent is open and then they suggest that when you finished your session (if you're not blown out of your tree that is) regass at very low pressure and vent off the oxygen. Has anyone tried this and how does the beer go after being exposed to oxygen for maybe a couple of hours at a time?
The only reason i can see you would do that is if your pump isnt fitted with a demand valve.