This is really of interest to the Bambi owners as there has been discussion as to whether and how the holding tanks are heated. I have been installing a "brand new" Thetford Thermasan system in my rig (Thetford actually stopped selling them back in the 80s due to high cost low sales...I will post the installation story and some pics once I am finished). For those that don't know, the Thermasan was a patented, independently certified (National Sanitation Foundation) system that pulled filtered waste water from the holding tanks and BURNED it in the vehicle exhaust just behind the catalytic converters where the temps are 200-300 degrees above the total destruction point of viruses, bacteria and odors. These systems were installed on virtually every GMC motor home of that time and Airstream actually offered it as an option during the early 70s. The system only adds about 2 gallons an hour of water to the 25 or so gallons an hour that burning gasoline or diesel fuel produces. I found two of the units in original packaging on eBay, knew what they were, so took the gamble that I might be able to make one work (only paid $100). Anyway, I am almost finished, just have to build a circuit to replace the old mechanical speed transducer that Thetford used back then (not an issue for me as I am EE). As a side note, I have found that the pump is still made and all parts are available, so the rest is actually just tubing and stainless steel, not much that can go wrong
Anyway, back to the subject. Since the installation required me to "invade" the black water tank and install a screened extraction probe, I had to remove the lavatory front section (it comes out without removing the lavatory or top surface). This not only gave me easy access to the black water tank (man did I have to think awhile before drilling that 1 1/2" whole in the side of the tank), but it provided me with a perfect view of the heating duct to the tanks. The duct is directed thru the subfloor directly into the belly pan area just above the gray water tank. The black water tank is partially above the subfloor and partially in the belly pan, while the gray water is totally below the subfloor. The heat simply circulates around the gray water tank and then back into the trailer via the space around the black water tank where it passes thru the subfloor. This actually is a good setup as it ensures circulation around both tanks. So, while the limits of freeze protection that this provides is unknown, the two waste tanks on the Bambi are certainly heated. A side benefit of the arrangement is that the plumbing associated with the shower is also in the heated space.