Welcome to the forum Dave! Yes, it should be tight. Can you tell if the overflow elbow is in the pond bottom or suspended ? To use any type of sealer you have to go swimming in the pond, or pull up the vertical overflow pipe out of the elbow to let it drain down so the elbow is at the water surface.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).