Full disclosure, I am not a plumber.

Do you have a tap below the level of the exterior faucet, such as in the basement?

You can turn off supply to home, open a tap on an upper floor, to vent, open exterior tap, and tap in the basement. Gravity will do what gravity does, but you need to allow it to vent.

Some low pressure compressed air can get the last of it out, from the exterior tap into your home, if there are any traps in the line that may prevent gravity from draining it all. If there are no traps, this would not be needed.

When done draining, turn off the exterior tap, and the interior shut off for the external tap, then close each other tap (upstairs and basement), then turn your supply back on.

You are also going to need air to get into the line, or the shop vac is pulling on one side of a hydraulic cylinder, the water will win.

Get some of the smallest diameter tubing you can find, feed that into the pipe, as far at the shutoff valve if possible, the use the shop vac, should be able to get most of the water out.

Once empty, get a Sharkbite bleeder valve.

I don't know shit about fuck, but it I don't think a shop vac is gonna clear water out of the line. If it were me, I'd cut off water, open the spigot, and also open some other tap further up the line. Then I'd jam a blower nozzle on a compressor into the spigot and blow the water back up the pipe. Maybe wrap some duct tape around the nozzle to get a bit more oomph on it.

Turn off the main water supply to the house. Also, close the supply valve to your water heater, just to isolate it.

Open an interior tap. Backfeed compressed air (about 20-40PSI) into the spigot. This will push the water down the supply piping.

When air starts spitting out of the interior tap, close the ball valve for the exterior line. Turn on the house supply, wait for the air to burp out, then shut off the interior tap and open the water heater.

You need somewhere to be sucking the air from or you won't be getting that water out.

Conversely, most water supplies are blown out for winterization. If you can apply compressed air somewhere and blow it out the tap.

A previous post talked about a foam cover and if you are in the home this is the best option ( aside from a frost proof valve ) if you are not there and using water this method is useless.

They look like a foam breast and attach to the valve with rubber bands and seal against the house. Or they have a string you tie around the faucet and then you cinch it up against the front of the foam. They work perfect and I have used many times for friends when I was unable to help them install a frost proof valve, which again is the ultimate solution.

Worst case and should be avoided is to wrap blankets/insulation around the valve with duct tape and let it drip, which usually prevents freezing.

What does the line supply? If you open the tap just a bit, all it takes is a slow drip, it won’t freeze.

1. I don't recommend SharkBites for permanent installations. Search here, you will see many of the same opinion.

2. I don't think you will get much water out with a vacuum. You might take the valve apart (i.e. unscrew the top portion) and may get a little more water out.

I'm in the North East, I've purchased foam covers for the outside spigots. Google "outdoor spigot covers for winter freeze protection"