I did about 1000 ft of 3/4 PVC water pipe and 10 gauge electrical wire. The ground was fairly firm, and there were occasional large tree roots (even though I tried to skirt trees by at least 20 ft). I first trenched with a subsoiler (if you hit a large root or rock, it's a lot better with a narrow subsoiler than it is with a larger, but much more easy to bend, middle buster, aka potato plow). Next I ran the subsoiler over the middle buster furrow a couple of times, and I still had to clear up loose soil from a number of areas with ---- a shovel. As to laying flexible pipe through a conduit attached to the rear of a subsoiler shaft - it works, but it works a heck of a lot better for narrower stuff, such as electrial cable. Good luck (and naprosyn, aka Aleve, sure helps the evening that you've worked on a trench).