We've put a lot of 20mm pipe in with a mole plough here on the edge of Dartmoor this summer, we found it best to do one run first without the pipe to make sure there are no rocks in the way or if there are find a way around, we then follow that line with the pipe in place & just before we get to the end of the roll dig a short 18 inch trench in front of the tractor to mole plough into to put in the joint & leave it uncovered until water pressured up.