Bottom Drain

I am in the process of finishing up with my new pond bottom drain. I have
used approximately 30' of 3" ABS pipe from the center of my pond to a
gravity fed vortex tank. I am using a TETRA bottom drain which I have
enclosed in concrete (2' x 2' x 2').

At a recent water garden show someone told me that I should not have used
ABS/PVC pipe because bacteria will form inside the pipes causing them to
clog up. Is this true?

Also that person stated that flexible pipe should be used instead of the
solid pipe. I used ABS as opposed to PVC beacause a plumber friend of mine
stated that ABS will withstand the cold weather here in NE. Any comments.

One final question: I am using stone dust underneath and around the pipes
leading from the bottom drain to mthe vortex. Anyone ever experience using
stone dust to fill the bottom of your pond? That is what they use to do
inground pools here in NE.

Another thought: what are the chances of the bottom drain
breacking/splitting at the junction between the concrete and stonedust?

Rich Holub in Massachusetts