The loose plunger part with clearing rod broke, so I modeled a new one. Afraid of the new one breaking the same way (and to avoid internal supports) I tilted the model 45 degrees. 

Print in the orientation pictured (horizontal touchpoints)!

Use petg or such filament, the custom support can be quite lightweight but the part itself should have 3-4 perimeters and +25% infill. The o-ring grooves should be supported with “normal” supports, I used organic (tree) supports.

 The hole for the clearing rod is really tight, I used a hammer to seat it. I guess you could enlarge it (or drill it out), superglue should work fine there. The rod must be in correct depth in order to clear the nozzle without sticking out when in use. 

Use the original O-rings or replace with 13mm internal diameter (18mm external) 2.5mm thick O-rings. Should not need any special heat resistance 

Feel free to modify the included f3d file for your desoldering pump and post as a remix!