this is when I am glad that I rent.

The faucet on should keep the inlet pipes from freezing, so now the worry is that the drain pipe will freeze?

If yes, how deep in the ground is the drain pipe?

If more than five feet, don't worry; you're in Maine, not Nunavut.
If less than five feet, has it ever frozen before?

If yes, set an alarm and run a couple of gallons of hot water every two hours.
If no, take a sleeping pill.

1/2 copper pipes in the evil crawlspace.

The waste pipe should be fine, thank the lord. Not only is it some variety of plastic, I put pipe insulation around it (pink stuff at the bend, though) while it's still above ground (under the house; and it goes underground, 5 feet down, under the house).

I stipulate that this concern may not be rational.

to deserve being addressed.

Simple fix for tonight is to open all the cold water taps a hair, pretty unlikely flowing water will freeze.

Another trick, used myself a thousand times to keep a car left outdoors from getting to cold to start, is a droplight with a hundred watt incandescent lightbulb. You'd be surprised how much heat that puts out.

Did you ever get that space heater? If so, will it fit down in the crawlspace?

Longer term, get yourself some heat tape. Easy job, spend a buck extra and buy the kind with a thermostat. Hook it up, plug it in and never worry again.

Good luck, pleasant dreams.

or put a small electric heater with a blower in the crawlspace, or duct warm air from the furnace into the crawlspace.

Should have taken care of this issue when you were down there the last time, eh? Your sin was half-assing the job, and your penance is having to go back under like Orpheus and perform for the underworld gods. It will be good for your soul when the job is finished properly.

I don't like a heater under the house, too much current draw, wasted energy and too high a temperature. I'm sure it can be gotten away with, no offense, but it isn't the safest or most efficient way to go. Heat tape with a thermostat is a decades-long-no-more-effort solution, although an annual inspection is probably a good idea. In my experience I only looked at the tape when I had to go into the space for some other reason and there was never any problem, but I'm lazy that way.

Take a look at the link, follow the directions. I find that running the tape linearly along the pipe works fine and gives greater linear coverage. You can jump from pipe to pipe with the same length of tape; with the insulating foam on top, it only takes a foot or two to provide enough heat for many feet of copper pipe run.

If you have claustrophobia, many people do, ask someone to sit at the opening and talk with you while you're underneath. An hour or two and you'll be done, no more sleepless nights of unreasoning fear.

Not about the water pipes, anyway.

Thought I remembered you have a droplight, so there's a good solution for the short term. Assume at this time you've already committed and gone to bed, but for the record it does have to be an incandescent bulb; fluorescent ones burn too cool to do much good. A 25 watt incandescent bulb is better for this purpose than a 100 watt fluorescent.

Good luck, ask again if there is anything more.

If you drip water too slowly, it can create an icicle within your waste drain which grows and grows, and eventually blocks your waste drain. This is the more common form of "frozen" pipe in these cold, nether regions. It also is why it is especially ill-advised to run plumbing in exterior walls: you can hold the thinner supply lines on the inside of the insulation, but there is usually less room to hold the thicker drain pipe on the insulated side.

Of course this is compounded by colder temperatures and keeping your thermostat low.

your ground temperature stays below freezing for an extended period, lambert.

you don't need to waste water to protect the pipes.

I'm not a fan of heat-tape 'cause I'm paranoid about electricity and water in proximity, but I'm not an engineer, either. More insulation is never a bad idea.

If you should suffer a frozen line, remember the key thing about thawing: gradual is better! (and cut off incoming additional water if you can.)

I assumed any under-the-house outlet would need to be GFCI to meet code.
But YMMV, and I only speak of the damage wet pink insulation that contacts a hot wire can inflict from experience. But that was 1987, dead of winter, under a trailer I was trying to live in with two kids while I worked for the local newspaper an average of 60 hours a week, in Big Spring, Texas.

Warmest thing about that whole stinking week was that shock, actually.

I'll get you a Taser for Christmas - so you can relive the warm memories on demand.