Plummingathome, as I interpret your inquiry, it sounds like the elevation of the sewerage outlet pipe is too low to allow the sewage to flow by gravity to the public sewer main. If this is the case, then the appropriate solution to the problem is to install a sewage ejector pump, and lift all of the sewage generated in the house to the required elevation to allow for gravity flow of the sewage to the sewer main. If the sewage ejector pump and pumping pit is located in the basement, or crawl space then there is no need to protect the pressurized portion of the sewerage pipe from freezing. However, if the pumping facility is to be located outside of the house, then that portion of the sewerage pipe that is full of water at all times, and is above the maximum estimated frost depth, must be protected from freezing with insulation and an electric heat tape.
An alternative to the use of the electric heat tape is to install a vacuum breaker valve at the apogee of the pressurized portion of the sewer pipe, and use a pump that allows the sewage to flow back into the sewage pit when the pump turns off thereby draining the pressure sewer pipe. Be advised that the vacuum breaker valve will require frequent maintenance so that it does not become clogged with sewage. If the vacuum breaker valve becomes clogged and does not allow air into the pressure sewer pipe, and it is below freezing, the sewage will not drain back into the pumping pit, and it will then freeze solid and potentially causing the pipe to burst.