Low ISO.
Small enough aperture to get the DOF that you want.
Shutter speed as long as you need to paint your subject/the background (could be much longer than 30 seconds)
Try playing first, before you head down there, while these are great suggestions, each situation is different, you may find you can boost your ISO higher without too much more noise, that f/8 is too high or too low, or that 30 seconds is producing photos that are too dark and you'll either need to boost your ISO or drop your Aperture.
While we can give suggestions, nothing will really compare to using your gear, download the manual, read it. Test it. Your house gets dark, you can test similar light conditions on it to drains / abandonments. (some say my house looks like a mix of both at times)
The other thing that hasn't been mentioned is none of this auto-focus pansy bullshit, it doesn't work in the dark. You'll have to learn to focus manually, with very little light.
Also, if you're shooting in a drain, there's no light, in abandonments there's generally ambient light, spend long enough and that street lamp a few hundred meters away will light up your whole shot. But in a drain. Nothing. You'll have to learn to light paint, evenly distributing light from front to back.
You'll also need a tripod, and to know how to use the shutter timer.
So much to photography, especially low light stuff, but the best way is to play, and remember, ISO low, aperture high and shutter speed as long as possible.
With my Canon G12, for long exposure in drains, I generally used the lowest ISO (80), but this could be much higher on an SLR (or CMOS lens camera) without making the photo to noisy.
15s, which I think is its maximum exposure, was usually more than enough time, especially with a decent torch.
And the aperture, I would usually have of 4.0 or so..