Hi, I'm a newbie to this site. So, I'm in process of unearthing an old water feature on our property. The feature includes a plastic basin (approx 3x6x3) at the top. Water would then travel down hill into two large ponds approx 6x8x3 deep. Everything was completely filled with rock and dirt but I've since dug out the upper tub and two basins to reveal the rubber liners on the pond floors. So, I expected to find a sump basin buried in the large pond but nothing. The upper basin has a drain valve on either side and one on the bottom. I ran some water through one side and the water came out the other side valve. Bottom drain is still plugged. It's probably about 10-15yrs old. Any suggestions on what to look for to figure out the pluming? Would water return from the lower ponds into the bottom drian of the upper basin? Sorry for the long posts but any suggestions would be appreciated!