Keeping Gray Water Tanks from Freezing During Winter Usage
My girlfriend and I have owned our 1998 Blue Bird All American RE for about a month now. It was almost entirely built out by the previous owner and I have some questions regarding his plumbing configuration and how it applies to our planned full time usage this winter. First, some system basics:
- 65 gal plastic fresh water tank in the living compartment underneath the bed located in the rear of the vehicle. It is right next to the engine-hump and is relatively well insulated.
- 35 gal plastic gray water tank located in the rear undercarriage storage bay directly beneath the shower. The shower pan has a short run of PVC pipe that protrudes down from the drain, transitioning to flexible drain hose that forms an "S" to the tank.
- 25 gal plastic gray water tank located in the front undercarriage storage bay beneath the kitchen sink. Same configuration here, except the PVC run is slightly longer and goes at a diagonal from the sink before passing through the floor.
The storage bay is unheated, and I am concerned about gray water freezing solid during the winter! We are located in Western MA and temps routinely go down to 10-20° F from Dec to March. I have some theories about how to prepare for this:
- Adding 20-40lbs of driveway ice melt into the gray water tanks immediately after draining and preparing to refill them. Gray water would mix with the salt, forming a high concentration brine that would freeze at a significantly lower temperature than plain water. As this product is routinely used on the streets, I imagine it must be safe for plants/animals/water table, and should be ok for all gray water dump locations.
- After shower or sink usage, pouring a small amount of concentrated marine grade PG or EG based antifreeze down the drain, to resist freezing in the "S" of the plumbing. I believe that this S is integral to the design, to inhibit smells from wafting back up from the tanks. If this is not required, then I will redo the connection and eliminate the "S" altogether. Please note that no food waste ever goes into gray water so I don't know what to expect for smells from soapy body wash rinsate.
We will not have a reliable shore power connection, and so tank jackets or heating rods are impractical.
Looking forward to hearing some people's recommendations and experience!