loud overflow, need help

[TANGOMAN]

I don't know that you'd find a noticable difference between ABS vs. PVC. I've got one of each on two different systems. Does that make sense ? No preferance in terms of volume...
I found that increasing the number of bends in "overflow lines" reduced noise. I also experimented with reducer bushings to slow the rate down without flooding the main tank. That's almost as controversial as a ball valve...something I wouldn't trust. Reducer bushings have a tapered edge. I believe that greatly reduces the risk of blockage.
I never heard of the "sliming" results but it sounds logical to me. Also, saltwater will have a definate sound difference compared to freshwater.
I wouldn't worry much during your "test run". (A wise move).
Experiment with different arrangements after a while.