A cheap solder sucker I got some time ago lost the ability to pull a vacuum.  The O-ring on the plunger failed to made a good seal. the slightly bent shaft may be partly to blame for this.  The easiest solution would be to use a larger o-ring but I didn't have any suitable replacements.  I then tried a few things on the O-ring to cause it to expand including some isopropyl alcohol which failed.

I then thought about putting some material in the space that the O-ring sits in to stretch it out to make a good seal and for the packing material I turned to this . . .

Yup, floss.  I wrapped it around in the groove that the o-ring sits it.  I had to go back and add a bit more as  I didn't add enough the first time around.

I then put the O-ring back on and greased it with a bit of Vaseline.  After all of that I re-assembled it and it once again can pull a vacuum.

And it's back together!

Side note: I wish that I had a proper desoldering gun/station (desoldering plated thru-hole components can be quite a pain) but can't justify the cost of one to use for occasional jobs.