Remember that my experience is hunting bad guys from helicopters with a search team (including canines) on the ground. I used my NVG and Infrared to find targets which I would direct my ground teams to search.I've had guys hide in drainage pipes and I found them. At first, I can't see them. But if they stay there for more than a few minutes, I start getting the heat coming out of the pipe. I've found many bad guys by sending my canine unit to search a "suspicious" heat signature in barrels, pipes, garbage cans, dumpsters, sheds, covered boats, ect.
My other flight experience and training is (w/DEA) looking for buried grow houses. They have their own signature. But Heck, they may not even be looking for you, and they may not even be a military or police type. You don't have to worry about every chopper, But if you hear one, hide. Wait for it to go away. Keep an object between you and the helo at all times.
Back to drainage pipes. To be successful, get as far as possible back inside (away from the opening). If you can plug the pipe to keep your heat inside, do so. But remember that ground search teams will look in all pipes. (good reason not to use existing pipes... they are under every road, driveway, rr track, ect [vry predictable]). If you have a specific place that you may use, camaflauge the opening. Make it a planned hiding place and go to it when needed. Heck. Just buy yourself a piece of pipe big enough for you and your gear and go bury it in an out of the way location. Then camo it real good. Hide all trails that go in or out of it. Put it in, or near, a place that can confuse a canine (use your imagination). Remember that a good canine will track your scent, right to where you are. So do your best to confuse him. The best way? Other dogs. Have your own kennel with several dogs. Bury your pipe right under their kennel. Cammo that entrance real good, cause the gestapo will be walking all around with flashlights looking for you. But their eyes will be mostly on the other dogs and kennels. They will think you are hiding in a kennel with a dog. And all those hot dogs moving around an barking, will keep any IR confused.
My feeling is that (if you don't have a planned hiding place) it is best to keep moving. Use the helo, or sounds of the trackers to know where "they" are at. If that helo is overhead, you better hide good. If it is a ways off, keep moving. Remeber, they can't see you, if they are looking in the wrong place. Contrary to popular belief, you can outrun most police dogs. Not, if the dog has eyes on you and he is released, but if he is tracking or trailing you. It takes most canines time to "work out" your scent. I think the exception is the bloodhound. He may move slow, but he is relentless. Unless you are a marathon runner, you better just shoot the dog and keep going.