The fill probe for the PP900w was actually designed for the pp700 pistol. The pp700 has a larger diameter cylinder so if you push the fill probe fully into the 900 cylinder one of the sealing O rings pokes out the other side. This causes a massive leak as you describe. The fill probe supplied for the 700 has two extra O rings making 4 in total. The two extra O rings stop you pushing the fill probe in too far. If your fill probe doesn't have the two extra O rings then just don't push it in all the way.

https://www.flickr.com/photos/288792.../shares/5557SQ

this shows my fill probe with all 4 O rings. If I try to fill my pp900 without all four O rings and push the probe in all the way than it will also leak badly