What I did was not try to fight getting the rubber cork 'over' the [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98]BM[/words] tip, but rather remove the entire [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98]BM[/words] valve assembly and stick the cork in its place. It almost fits perfectly, but will need something (I used a rubber washer) to keep it secure while you're filling the cylinder with water. Once you've created a seal, the cork stays-put due to the vacuum.