Sorry you can't sweat galvanized or threaded connections. But you can add a threaded adapter to a piece of copper and screw it into a bath faucet. What I typically do is to sweat the adapter on to the copper, then let it cool. Once its cool I thread it into the faucet with some pipe dope. Then I create another piece exactly like the first one and screw it into the threaded pipe on the outlet from the floor (or wall). In between the two pieces of copper I use a compression 1/2 inch id (5/8 od) coupling. This allows you to connect the two pieces of copper together without sweating inside the access pannel to the valve. Always make sure you clean and deburr the end of your copper and clean the inside of your fittings with a copper fitting brush. Then liberally apply a self cleaning flux to the inside of the fitting and the outside of the pipe. When you do solder, make sure you use mapp gas and a map gas style turbo torch. This will provide you with enough heat to solder your fittings properly. Since solder enters the fitting through a process called capilary action, if you apply the solder on the opposite side of the fitting from the point of the torch, the solder will flow to the flame of the torch. This tells you that you have heated the fitting all the way. And as soon as the solder starts flowing, like water, then move the torch to the next part of the fitting or you will burn your joint.