[cm1js]

I am supposed to have a box with a tub drain roughin under the concrete in my basement. The rest of the rough ins were above the concrete. I am trying to figure out the best way to find this box by drilling several small holes in the concrete in the general area where the tub was planned. Since the contractor wants the work he won't tell me where the box is exactly. How deep normally are the boxes and how do I find the pvc under concrete so I don't hit any drain lines and have to tear up the whole floor. I have tried witching but so much water is under the floor it's impossible.