Laying pipe on surface saves a lot of work, but we found in the hot weather we had this year that the cows were thirstier than normal and crowded round the tank...the pipes were softer than normal and with a few hooves on the pipe, water stopped flowing altogether, leading to more cattle round the tank and on it went. Had the mole drainer/pipe layer out since then to bury pipes safely away. Very thankful for concrete tanks, they'd have trashed metal or plastic ones