Interior French drain Watertown is generally installed using a sump pump in the basement to fix or stop flooding. Interior French drain is dug and buried more deeply into the ground, typically 5 to 6 feet, so they are costlier. The installation process by a building contractor could be very labor extensive and requires a massive moat be dug within the home’s foundation. The total standard cost is $50 up to $60 per linear foot. For a 20’x30’ basement, the perimeter is 100 linear feet, which suggests that the total installation cost would be around $5000 to $6000. Basements with lower than 130 to 150 linear feet only require one sump pump for an average cost of $175 to $225, while much bigger basements usually require two sump pumps.