We picked up a Super Soaker D5000 at a yard sale yesterday. Unfortunately it wouldn't pump up.
I removed all of the screws holding the two halves together.
Then I used screwdrivers to pry that orange cap off (to the right). It has a small lip that retains it.
The plunger o-ring was a bit worn/dried out so I replaced it with one from my handy O-Ring Assortment Kit
. It's a pain to press the orange cap back on, pressing it against the edge of my bench worked best.
Now it works.