Oh it gets worse than that. Need to get an old fire extinguisher the kind you can pressurize with the air compressor put a long piece of 1/8 copper tubing on hose fill it with boiling water open septic tank get the tubing inside outlet pipe and start melting if your lucky it won’t take much. One very important detail I forgot to mention is ALLL valves in trailer MUST NOT LEAK! I repeat MUST NOT LEAK. A slow slow trickle of water will freeze and plug pipe. It might keep your potable water from freezing but your drains will. If I had to do it over I wouldn’t buy a trailer. I would build a garage slab on grade live there till I could build a house then you have a nice shop and no mobile home ****.