Hmmm methanol in sewer pipes. Nope. Not a good idea. It could melt the pipes and or the fumes could cause one hell of an explosion.
your best bet is to thaw the pipes. A small electric heater placed near the frozen pipes would do the trick. Be sure that it is not near anything that will catch fire. If you don't have one an infrared light bulb pointed at the pipes will work but it will take a lot longer. You can get one at your local home improvment center for around 5 - 10 bucks. An old lamp works for the socket. You can get one cheap at any thrift store.
Once you get them thawed you will need to insulate them. Most construction sites have a chunk or two floating around that you can ask for. Wrap them up and use a piece of string or some tape to hold it on with.
I hope this has answered your question. If it has then please be sure to click on the accept button.
Best regards; The Home Smithy.