Make a loop in 600 mm of a single core of mains flex cable or better still something like strimmer line , tie the ends round a bit of dowel to make a pulling handle.
.
Insert the loop 150 mm in the bottle , Invert bottle , shake it and gently pull so the cork /bung is caught in the loop at the widest end so the small end is facing the outlet . When you have trapped it well , keep pulling gently but firmly and the cork / bung will come out .
If you squeeze a tiny drop liquid soap in the demijohn's neck it helps lubricate things so even the most awkward of bungs and corks come out easily .. I must have done hundreds & hundreds when I was making SodaStream concentrate back inthe1981 as almost all the demijohn's of super concentrated flavour from Bush , Boke & Allen had cork bungs under the screw on caps , the quickest to empty up to 20 or so single demijohn's of colour or concentrated flavours in the demijohn's was was to knock the bung in with a wooden peg and rubber mallet .
I was allowed to have the empty glass demijohn's FOC. which I took home most days , de bunged them , washed and drained them , same with their caps , then sold them as wine making demijohns' in batches of 5 for £2.00 to a local home brew and wine making requisites shop .
