I've had two 2018 floor plans, DS and now a MA. When we are in cold weather there are two water lines I address. The hot water line in the generator compartment you are asking about and the water line for the frig that runs outside under the full wall slide. I attach an air compressor to the water hose and apply 20 psi. Run the water dispenser on the frig door until nothing but air comes out. Then do the same thing with the hot water faucet in the generator compartment. Be careful that the OASIS burner, AC1 and AC2 are all OFF when you blow out this line because you are going to empty the hot water supply within OASIS. Once both of these line are clear, turn off the black shut off valve for each line. They are located together up along the frame rails in the pass through bay just behind the house battery bay. Now run the hot water faucets in the kitchen and baths to refill the hot water lines running through OASIS.
The water line for the frig is wrapped with an electric heating tape. This is activated by a control module located in the house battery compartment. It has a red light (off) and a green light (on) and is suppose to turn on when the temperature gets below 32 degrees. I have checked this in freezing temperatures and it did not come on. I since moved the module to up under the hood in more open air and it seems to work better there. Still don't trust it. We don't use the water in the door of the frig anyway.
2020 Mountain Aire 4018
2017 Dutch Star 4018 (sold)