Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5100733.
UPDATE 10/Nov/2021
Added models for a filled version of the piston to make printing easier for people who don't care as much about the part being a replica.
This is a model of the pneumatic pump assembly off the 1989 Kenner, The Real Ghostbusters, Ghost Trap.
I have modeled this off an existing, intact, assembly. This will allow you to print off replacements to restore the toy. The main body of this assembly often gets cracked, causing air to leak out of the cylinder rather than push the piston to open the trap doors.
There are 2 versions of the main body. One is a replica of the actual part and the other is the same part without the nipple so that you can install your own, if you wish.
Parts have been tested on an FDM printer and work properly.