I have about an 8' length and a 5' length of 8" green PVC sewer pipe. I also have a 56" length of 12" pipe.

Looking at applying the bucket structure concept to the pipe and make "logs" using 1/2" drip line tube.

So the question is do I leave the ends 100% open or do I try to block them off and only add small openings?

On the 8" I figured that the tubes could be arranged extra densely to block the end somewhat to keep the larger fish out, but the 12" would be far more challenging. The 5' length already has gasketed caps on it. I used it as a tank at one time.