This is both a culvert drain and one we drive over.
I'm beginning to like the idea of the black plastic slipped inside the exisiting galvanized steel. However, as you can see from my "hijacked" post earlier, my husband is very concerned about the rust continuing if it's not stopped. Perhaps we "stop" the rust with whatever product that might be, then we insert the plastic.
How in the world do you insert 40 feet of plastic without damaging it - cracks, holes, etc?
