I'll try an oil extractor pump first.
Seem you connect up the filter except for the centre pipe, attach a pump and suck/pump until the filter is full...or you can use a syringe or funnel and fill it from the top.
Apparently you should change the filter every 10K or so according to what I've read and the chap at the garage highly recommended changing it regularly.
I bought a filter around 30K miles ago but never got round to changing it, despite having done 2 services and replacing 2 injectors in that time
. and who knows how long the current one's been on there
P.S As suspected it was the 2 remaining injectors so that's another £500 aka a months fuel expenses