Gravity Drains not Draining

I recently camped in Colorado (-5F!) at a full service campground.

I thought, "Hmmm...since I have water and sewer, I'll fill the inside tank, and use it when I want to shower, and then run outside and open all the low point drains and drain valve for the shower when I finish. I should be able to use the toilet normally, so that's cool."

I discovered some flaws in my thinking.

1st: In my TM, it seems like gravity draining (with open faucets and head removed) does not help the inside shower. Something froze in the lines going to the shower, and it was frozen when I started camping (I leave the low point drains and faucets/showers "open" all the time when I don't have water, so they had literally been open for a month or more). I was able to thaw it, but it quickly froze again after I drained the low points.

2nd: I didn't consider that the drain valves would freeze. They can and do. This was a minor annoyance with the gray water, but a big deal with the toilet. I didn't think with the toilet, and pulled the inside valve before trying the outside one. Fortunately it warmed up before things could freeze in that pipe. I had dumped some pink stuff down all the drains and the toilets to keep this from happening, but clearly I didn't dump enough, and I didn't consider that the ice would form on the *outlet* of the dump valves.

3rd: I assumed everything had traps in the gray water system, so there would be no oders if I left the gray water valve open while connected to sewer. That was VERY wrong. Don't do that, learn from my mistake! I thought I could leave the valve open and worry less about it freezing closed.

When it is warmer, I'm going to look at the pipe under the trailer and going to the shower. My suspicion is that it runs horizontal at some point, or maybe slightly "uphill" to the low point drains. I know that the water pipes under the sink do that and won't drain in my unit from the low points (I have to fix that!). I'm also going to seriously consider the heated valves, drain pipe (just for the gray water, don't think I need it for the black water pipe if I have a heated valve), and heat pad on the gray water tank. But I've got to think about how often I camp in these temperatures with hookups (it would be impractical to do this without hookups) and how inconvenient it is *really* to not use the campground facilities when available.

I think my toilet problems could have been solved easily - if I started with the toilet valve open, but the gray closed, and didn't use the gray tank, I think I could have easily managed dumping and such of that tank, so I learned an important lesson there.

On the other hand, the heater works great in the TM - I had a problem with not being able to completely drain the propane tanks due to the cold, but I was nice and toasty inside.