How do I not blow up my city water connection check valve?

After getting antifreeze absolutely EVERYWHERE else, turn off the pump, and open the kitchen cold water faucet. That will depressurize the water system. Leave it open as a vent, and go outside and depress the plunger on the shore water inlet. There is no pressure to blow the gaskets off, but the gravity flow of antifreeze from the kitchen faucet will flow antifreeze through and out of the check valve. Then, go back inside and turn off the kitchen faucet.