After cleaning both tubes a level of clean reserved for operation rooms I applied the flux
To keep things from shifting you need a little weight to tack it down. Weight is where you find it.
This tack got a little hot. That's why we practice right. Normaly I'd tack this joint in 4 places, and I'd have a fixture to permit that, rather than a could weights. . . . It's Practice.
Then I tin the joint. It's basically a thin layer insuring it's sealed. Also you turn the torch up a bit more than you do when you lay you fillet.
Then I lay the fillet.