flushing out the antifreeze

I for one am glad you are asking questions. We haven't received our RPod yet but expect it at the end of the month. I have started a file that contains all the "how to's" I am finding here. Thanks for asking questions. I am looking forward to the day when I can answer some of them.

techntrek:  when you mention 'low point drains' are you referring to the valves you open to drain the gray and black water tanks?

The 'low-point' drains are small diameter (usually white plastic) tubes which hang below the RPod.
They are used to drain the water out of the fresh water pipes when winterizing the Pod.  Usually the drains are ended with small twist-on caps.  Spin them off and water should drain out.  If the Pod is brand new, the factory used compressed air (no water) to test for leaks and make sure that there was no fresh water to freeze in the lines.  A Pod that has been winterized with RV antifreeze should have a small amount of pink water which will drain out of each low-point drain.
Don't forget to drain the hot-water heater...usually the tank is drained and left empty using the heater bypass pipes when winterizing.  If pink water comes out of the heater drain...someone didn't use the heater bypass and you will have to flush out the water heater tank also.
I found that even after draining the antifreeze out of the lines, the glycol antifreeze will leave a slight taste to the stored water, even after several flushouts/uses.  There are several water-taste treatments sold which claim to kill the taste but if you check the bottle contents, it is usually a bleach component.  So you trade a glycol taste for a chlorine taste. 
I treat my fresh water tank with an RV chlorine water treatment solution each spring to kill any bacteria which may be in the water tank and purify the water lines. (it takes a minimum of about 3-4 hours sitting in the tanks and lines to be effective).  So I end up with either an antifreeze taste or a chlorine taste.
After a complete tank fill and water line flush and drain, I fill a gallon milk container with water mixed with baking soda and pour it into the water tank.  I then fill the tank enough to pump
the soda water through all of the lines (including the water heater tank.  I usually let the soda water sit over night and then do another complete drain/flush.
The soda water flush really does remove any residual taste to the water.

I agree that the Propylene Glycol does have some antiseptic properties.  I usually add the 'chlorine treatment into the freshwater tank in the Spring to kill any bacteria that might have grown since the Fall.  I don't add RV antifreeze to my freshwater tank...It would take a couple of gallons of antifreeze to reach the water pump tank outlet.  On my Pod, the freshwater tank drain is at the lowest part of the tank so there is only a film of water remaining. RV antifreeze is fairly expensive and I only use it via the 'antifreeze-winterizing' hose installed at the factory adjacent to the water pump.  Thus the pump and water pipes down line are protected without leaving antifreeze in the water tank and subsequent taste residue in the tank. 

aside from the hot water heater valves...is there another valve that needs to be turned prior to flushing?  i was watching a video today and it looked like they turned a valve to get the pump to accept the antifreeze?  where might that valve be on the 172T?  just dont want to break anything!