in my personal experience i find that, if you heat away from the female end joint about 3/8 of an inch, the solder will actually suck toward the heat and be drawn in (with the use of flux very necessary). also for my 2 cents those pre done fittings that have flux and solder in them are top notch. just slide on and heat nothing could be easier. but i am not a pro by any means, just done a number of my personal homes.