After several rain, I noticed a pond in my backyard. I made a concrete patio last summer with drain pipes underneath it. So, I dug some soil and got the one end of the drain pipe where two pipes are connected by a 90 elbow. Both pipes don't move at all as they are under the concrete. What I have to do is to somehow replace the elbow with three way connector so that I can add another pipe to it. Since two pipes don't flex, I cannot even remove the elbow. Any tricks to replace the elbow with three way connector without damageing pipes? Appreciate your advise.