Close those low-point valves and locate the back of the water heater access as well as the water pump. Your location may vary, but you probably need to remove a useless panel.
First, let's by-passs the water heater. There are three valves:
You should see the Hot and Cold open and the bypass closed.
Switch all three to look like this:
Next, find the water pump and switch the intake valves from fresh water tank to the open hose. You can see the two valves behind the pump here:
So now the pump will draw through the open hose. I use a bucket with 2 gallons of anti-freeze in it:
At this point you are ready to turn on the water pump and go around to every faucet. Let it run till the pink stuff comes out of hot AND cold. Flush the toilet and don't forget the showers.
Make sure to run enough to fill all the P traps and get some into the holding tanks. Make sure to go outside and push in the pressure valve inside the city connection. This is the white, plastic thingy inside where you connect the hose. This will allow the pump to flow anti-freeze up the city connection hose.**the pink stuff will shoot out at you!
Turn off the water pump and dump and remaining antifreeze into the drains/toilet.
The whole process should not take more than 30 minutes (15min if you're good)
and costs all of $6.
I think I covered everything.
This is only meant as a guide, so do this at your own risk.
To get it back to operational status, run fresh water through the pump AND city connection to flush all faucets.
THEN plug the water heater and switch it's valves back to fill it.
Good luck and DIY!