Ok 24 hours of being full of rust desolver did nothing to help.
So had to go at it the hard way and unsolder the cap that is on top, which of course burnt off the nice paint job I had on it.
Had to spread open the crimped end of the vent tube (the hole in the end wasn't plugged), stick a 1/8 steel rod down inside it and drive it through with a hammer
A pile of rusty red/brown powered came out the other end. After lots more roding and blowing I got it all cleaned out. Soldered it back together and not it is ready for another paint job
Moral of the story: Always check every line to make sure it is open BEFORE you go ahead and paint it and get ready to put it back together......