Use the cheapest white bread.
Do not use wheat, to much oil.
Open the vacuum breaker, remove the diaphragm and wash the bread through.

OMG ! You all obivously haven't heard what Klem says about "I Herd and Tha Syad",so here you are. Both lie a lot and you shouldn't believe everything they say.
Plumbers NEVER give away trade secrets but delight in blowing smoke up unsuspecting diyers.

If it's not the lowest point, open a lower valve (or many) and let that drip. Or blow it out with compressed air from an open valve above. Then work fast.

Ok, it worked for the faucet. The next project requires me to put in a "T" and both ends will be at freeze proof spigots. So how can I do that without blowing bread into the spigots?

I am thinking about sweating it all except using a "shark bite" for that tee???

A trick I've used plenty of times is vacuuming out the water pipe with a wet vac.

It works if you can get an air break into the line (say by opening a faucet someplace).

By the time the line fills back up with water, I have the joint soldered.

I've never used the bread trick - although I've heard about it.

BTW: This is why God made ball valves - for positive shut off years after they've been installed. Clearly someone else was responsible for gate valves - quite possibly my ex.

"quite possibly my ex."

And locks on gates.

The bread simply dissolves.

TAKE A SMALER DIA PIPE WRAP ELEC TAPE AROUND COPOER PIPE TILL IT FITS SNUG PUSH IT IN A FEW INCHES AS YOU SOLDER THE WATER WILL LEAVE THROUGH THE OTHER PIPE THIS GIVES YOU TIME TO REPAIR VALIVE