Since the old post got the PB treatment, thought I would post more pictures
Here I am knocking the plug out of a thermos pump. That is a 3/4" wrench, or you can just hold it in your hand. Takes a few good wacks with a hammer on extension and plug will come out.
Here is plug out. Has the "hidden 4th" oring that often leaks. You can see the NRV, we are gonna stick it in the hole. THe poppet has already been removed, just cut it with some wire cutters. You may have to enlarge the hole just a tad for the smooth shaft of the NRV to fit. A rat tail file works, or a chainsaw file.
Here is plug in vise, I am screwing NRV into plug. You can see some red locktite. Tap on cresent wrench and NRV and turn in slowly, it will sorta cut it's own threads. It goes in slowly.
Here NRV is in plug, with new oring. I have cleaned and smoothed the pump tube where plug goes in. Oring is Felpro #411 w 3/32, ID 9/16, OD 3/4. I didn't have the next size down, bet it would work fine too.
Here is how you test your work. Slip balloon onto pump, and pump it up a bit, see if it holds.