I live in a trailer in Arkansas (yes, cliché I know). Last week we had a very cold snap and the temperature was below 20F for a few days. Now the toilets in the house drain very slowly, if at all. The bowls fill all the way up to the rim. Plunging helps them drain, but will sometimes cause water to come back up the sinks or shower drains in the bathrooms. The whole house is affected.

The main drain for the house is under the trailer, not wrapped, and above ground for about 70 feet. It doesn't go underground until it reaches the end of the house. It feeds into a septic tank. I tried to find the vent for the septic tank and couldn't find it. I have snaked the air vents to the system (except the one that should be going to the roof, I can't find that one), I have snaked the drains, I've tried running hot water down the pipes, I've even tried rubbing alcohol to melt any ice. Nothing has improved the situation.

I think that there is probably ice in the bottom of the main pipe, constricting the diameter of the pipe and causing the toilets to drain slowly. How can I get rid of the ice? The pipes are metal but not readily accessible.