I have installed a french drain recently about 4-5 feet from the house using EZ-drain system. (my house was buile in 1968) I also have an interior drain in the basement w/o sump pump (my house sits on the hill and uses natural gravity to carry out the water.) How do I determine whether the newly installed french drain is working? There is a small gap (interior drain) between the wall and the foundation I can stick the finger. Thanks.