Air purge of fresh water system to winterize ?

[desertug]

In my RV trailer days, I would adjust my portable compressor to output no more than 20 lbs pressure hook it up to the system water inlet and after draining the pressure pump and the tank, blow air thru all faucets and outdoor showers. Didn't like the taste of RV anti-freeze, I used cheap vodka one year but didn't like the after taste of that in the tank and lines. Does the fresh water tank have a vent? I assume it does, can i just tape over it to pressurize the system and pour a little antifreeze in the sink drain for the p-trap? :idea:

 

[Osprey]

The tank most certainly has a vent line. When adding water to the tank via the deck mounted water fill fitting, the general practice is the continue adding water until some water starts to gush out of the hull mounted vent fitting. Simply adding water until the gauge reads full does not, for my boat, come near to filling the tank.
The water line from the city water connection has a check valve installed. When water, or air, pressure is applied to the city water connection, the check valve prevents the water or air from back flowing into the tank and out the vent. So if using the air blow technique of winterizing, there is no need to tape over the vent. However, air blowing will not protect the tank or water line up to and including the water pump i.e. from the check valve back to the tank. Further, from my RVing days, my experience is that the air blowing leaves some water in the low sections of the lines. After the lines are partially empty, the air tends to flow through the lines above the water. You need quite a strong air flow to completely clear the lines and 20 psi does produce the required flow. My view is that for full protection, RV antifreeze is required. However, once one has used antifreeze to clear water from the system, water tank forward, what is the point of leaving antifreeze in the system over the winter? Next spring a lot of flushing is needed to get rid of the taste that has permeated the lines and all. What I do is immediately after flushing with antifreeze, I use the water pump to pump as much antifreeze out of the system as possible. I then apply air pressure via the city water connection and blow out most of the residual antifreeze, check valve forward.A way to keep the required volume of antifreeze to a minimum, I have installed bypass valves to the water heater tanks, inlet and outlet lines. Use of these valves prior to adding antifreeze, isolates the tank from the rest of the system. With this isolation I find that 2 gallons added to the water tank is sufficient. The tank is easy drained and cleared of water so no antifreeze id needed here. Actually I use air to blow out the tank. Care needs to be taken that the hot lines, exclusive of the tank, are not isolated.

 

[Pilotnavigator]

I have the 21ec so my process will be different but perhaps provide some help. I have easy access to the water pump. First I ran the pump to empty the tank. Next I removed the line from the tank to the strainer by using the quick connect fitting at on the strainer. Next I removed the strainer from the pump.
I had purchased a quick connect fitting and attached a length of hose to it. I installed this line to the pump suction with the quick connect. The end of the hose went into the plumber antifreeze jug. I ran the pump and opened up the taps to flush. Once pink ran out I shut off the pump. For those with a hot water tank it should be drained and you should install an RV by pass kit on it. This works well for all the RV I have owned. There is no issue for the little bit of water left in the tanks. It will freeze and expand just like the ice in a ice cube tray. The tanks are vented so no issue. On the hot water tank you can leave the pressure release popped or as I do just leave all the tap turns on this will keep the system at atmospheric pressure. Then in the spring there will be no antifreeze in the tanks to mess up the water.
Use this info as you see fit. It works for me but your systems may be different.

 

[Osprey]

Except for my use of air, the method of winterizing described by John (Pilotnavigator) is essentially the method I used for about 30 years on an RV. However, the RV's water tank had a drain valve on the bottom such that no water was left in the tank. There is no such tank drain valve on our tugs. I agree that the water in the tank has room to expand as it freezes but I am less easy about the tank's output fitting and lines, and particularly connections, between the tank and the water pump. If frost damage occurred in these sections of a tug, access to make a repair would be a real headache. I do understand that I am in a minority with respect to this issue. What works for you works for you or at least I hope it does!

 

[Pilotnavigator]

Should have stated that on the 21ec the suction line to the pump is a straight shot down to the tank, so no water can be left in the line.

 

[tuggin aweigh]

I use a wet dry vac to purge as much water from the tank and lines. I then winterize the system in the normal way and use the wet dry vac once again to remove as much anti freeze as possible to reduce the after taste in the spring.
Tuggin Aweigh

 

[NorthernFocus]

There's risk involved in only blowing down with air and not using antifreeze. Making a mistake and destroying the water pump or breaking something that is difficult to get at would be a pretty high price compared to the minor annoyance of flushing a little antifreeze from the system. Or so it seems....

 

[desertug]

all good information. I think you are right minimal antifreeze may be the answer. Thanks