My simple question is, if I add antifreeze to a few gallons of fresh water in the tank and then run that through all the lines and fixtures before turning off the water pump and leaving the faucets open, why do I need a compressed air blowout? Or even draining the lines for that matter?  (I do not use the fresh water tank for drinking or cooking, BTW, and I live in a climate where low temps rarely get into the 20s.)

Thanks in advance,  Ely 

You don't have to blow out the lines. It just removes more water then simply draining with the low points, thus reducing any dilution of the pink stuff. Your method will work, it just takes a lot more anti freeze, because you have to get enough into the holding tank to reach the pickup AND be concentrated enough to work. There is almost always "some" water in the holding tank, even after draining. The simplest method of winterizing is to:

Drain the FW holding tank

Drain and bypass the water heater

Set the water pump valve to winterization position

Stick hose in gallon jug

Turn on pump

Open taps one at a time until pink comes out

Don't forget the outside shower if equipped, or the toilet

Pour 1-2 cups of anti freeze into all the drains, and in the toilet bowl

Have beer (optional, wine, bourbon, kool aid)

The whole procedure will use about a gallon or a little more.

I've done it both ways because I forgot to open them one time before running the antifreeze in. It really doesn't take much more antifreeze if you don't drain them, just a bit more run out the faucets to be sure its not too diluted, but I'd be afraid of leaving them closed and allowing plain water to sit in them all winter. 

Pushing70 - If you know someone who knows how to winterize your trailer, get her to show you how.  If you don't, then it's worth the money to go to an RV service place and have them do it with you watching.  Once you see it done, all becomes more clear.  The plumbing system is designed for easy winterization and once you learn, it'll only take a few minutes to do.

And don't worry about 70.  Once you pass that land mark, it gets even better. ;--)

I covered draining the low points in my opening sentence.

But.. I have had my low points freeze solid down to 0F with pure water in them, and it didn't hurt them. We don't winterize to protect the lines. The lines and "plumbing" are PEX, and PEX rated, so freezing literally cannot hurt them.

BUT freezing can/will/does damage the fixtures. Along about a week or two before memorial day weekend (start of the official camping and pool season for many), you can expect a run on pump filter housings, toilet valves, and outdoor shower fixtures. Happens every year.

BUT WHAT I TOTALLY FORGOT>>>

P Traps. You need to pour 1-2 cups of pink stuff in all the drains, and into the toilet bowl. This protects the "p trap". It's been 3 years now since I had to worry about them. Lance uses hepvo valves instead, so no p traps.

So, if you have an air compressor it's easy to build a fitting using a air pressure regulator from Harbor freight for less than $10. A regulator is needed to adjust the pressure to around 30 PSI(my compressor goes to 120 PSI, which will damage the pump and toilet valve). 

Screw a Camco blow out plug($7) into the City Water inlet. 

https://www.homedepot.com/p/Camco-Blowout-Plug-with-Quick-Connect-36143/205808403

Attach the air regulator and air hose. Drain the HW tank & fresh water tank, low points and replace the plugs, then open a faucet and turn on the air. Alternate the hot and cold kitchen sink until nothing but air comes out. Do the same with the shower wand, bathroom sink and toilet. Move the air to the Black Tank flush water inlet and blow that out too. Pour a little bit of RV antifreeze in the shower drain, toilet, bath sink and kitchen sink....done. 

HF parts needed:

http://www.harborfreight.com/air-tools/air-tool-accessories.html - regulator

http://www.harborfreight.com/brass-industrial-quick-coupler-set-4-pc-68241.html - couplers

http://https://www.harborfreight.com/14-in-male-brass-universal-coupler-63550.html - Male/female coupler

Once the water is drained, it's takes about 10 min to blow out the lines. Be thorough and you will not have any freeze damage issues. 

Just as a note..

If, during the camping season, you use your FW tank and pump, this method does nothing to protect the pump or it's filter.

While its much less likely to damage pex rubing from freezing than for example Cu pipe, it is certainly possible.

Bursting becomes more likely over time as the plastic ages and becomes more brittle, like all plastics do. 

I researched this when I replaced all the plumbing in my house with pex 3 years ago. We all have hose lines exposed to freezing under our elevated houses here. I drain those in the winter. I love pex but I'm not confident to leave plain water in the exposed low point drain lines in my pod. 

The other problem with pex is that it is damaged by UV exposure, so should never be left exposed to sunlight for long periods. Some of the longer low point drains hang down enough to get sun exposure at times. 

Personally, I think the best approach is just to remove the low point drains entirely. They aren't really needed for freeze proofing with either air or antifreeze and provide a place where the rPod plumbing is exposed to freezing, UV, and physical damage.  

Originally posted by JR So what is the purpose of the low point drains in the plumbing system on the r-pod - maybe a gravity winterization application??? I don't get it.

When there is no water pressure and faucet valves are open, opening the low point drains will suck most of the water out of the pod. Less water means antifreeze will be less diluted and have a lower freezing temperature.  Less likelihood of frozen valves or pump.

TT

Agreed, I haven't heard of in RV's it either. In residential use it seems like it tends to occur when an ice plug forms in the line and then the water between the ice plug and a fixture freezes and has nowhere to expand to.  I suspect it will get more common as pex ages. It has a stated life expectancy of 40-50 years if not exposed to UV.  Pex first came into use in plumbing about 20-25 years ago. 

My conclusion is that if you use the low point drains as intended then there is no freezing risk from them, there will either be air or antifreeze in them. If you don't use them then why not remove them, or as much of them as possible? If you do keep them then protect them (with pipe insulation or some other material) from UV and flying rocks, especially if they hang down about a foot like mine did. That seems ridiculous to me. 

I only use my tank and pump, rarely use the 'city water' inlet. I have not had a pump problem yet, but I always run the pump dry while blowing out the lines. Yes, there should be a way to run air thru the pump and filter screen.....good point. Maybe removing the FW tank bung and blowing air through there would move any line water up to the sink. 

Depends where you live. I only winterized about 3 weeks ago. We've had all of 3 nights get below 30 degrees so far, and the way its going we might not have any more this year. Its 60 today and will be close to 70 tomorrow. Good camping weather except that all the campgrounds around here are closed right now...