I have a small pond approx. 40' x60'. Just had a leaky wall shored up with 3 loads of clay. We upsized my overflow line to a 6" dual wall pipe (corrugated outside, smooth inside). Guess we did not pack it well enough and water is traveling along the bottom of the pipe. Since I have to re-dig it, I'd like to add some kind of anti-seep collar. Would concrete be sufficient? If so, any recommendations on dimensions and reg. concrete or hydraulic?