I've had pretty good luck (as an amateur) sweating 1/2", 3/4" and occasionally even 1" copper for various DIY projects around my house. Recently, I attempted to sweat an 1 1/2" trap adapter to a double ell (?) DWV fitting, both (I believe) made of cast brass. I cleaned all surfaces very well and cleaned/fluxed with Oatey product that contains tin. I use mapp for heat. The joint was horizontal, so I applied heat to bottom of joint, and touched solder to top of joint. It seemed to take forever for the solder to melt/run, by which time the entire fitting was black, and the resulting joint looked awful (no way I would trust integrity of joint inside wall of our new bathroom). At first it seemed that I was not getting the assembly hot enough, but in the end, I am guessing that I eventually got it way too hot. What went wrong?