I did something similar to this once before. i used 1 1/2" pipe but did not drill holes. I tied a piece of electric fence wire across a fork in a big limb. Put two or three on like this and the just used a tee with a couple foot long pieces of pipe glued into it for the top of the pipe sticking out of the crete. Just glued it on and it worked for a good cap. CF
The Original Woodsgoat Hater
2011 NWR Bash Yellow Perch Champion