corny head space

[newToBrew]

popping my corny cherry tonight - tomorrow night

have 25 litres of brew ready to go

how much head space should I leave in the keg ? - I ws thinking of putting in 18 litres & leaving @ 1 litre head space - is this ok ? what do u guys do ?

[Ciderhead]

Fill it to just below the gas dip tube. You can see it as you are filling it. Any more and you'll end up with beer in your regulator.

Near miss with that once and after the nanosecond cold sweat have a non return valve on gas which cost me a fiver, cheaper than a 35 euro reg.
Don't be tempted to do what you do to the fuel tank in your car!