I have used a disused LPG cylinder (about 5kg) with an old LPG valve with a dip tube (called liquid withdrawal) and an air fitting. The bottle can take about 300psi, but I use it at about 30-40 psi, charge it up, carry around and use plastic hose with an inline irrigation valve on the end. Can do 4 litres in about 5 mins. Problem is filling it up takes bloody ages and knowing how much you've put in can mean you get a fair bit of overflow.
Other option would be a standard LPG valve, but put oil in (somehow), charge up with air using usual gas outlet, then upend and oil will come out valve...fit a hose and ta-da...would have same problems as mine, time to fill cylinder and how much has gone in?
Having used this a couple of times, I am gonna convert a 4l container with the level indicator bit on the side.
Cheers
Rowan
