Hi Cheri I in the proses of setting my first system up too and all the things I'm finding is confusing at best. I'm trying not to over think it to much as the concept is strait forward. I think (key word) to have overflow drains bigger than the intake lines. I'm coming from my sump tank with 1” lines with a valve to adjust flow into beds. I have 11/2 inch lines to drain from my fish tank into a swirl filter then into a bio-filter then dropping back into the sump. My bell syphons will have ¾ stand pipe for draining. I will have a 2 inch pipe returning to the sump between the ¾ inch pipe and the 2inch pipe will be an inch or two this is called an air gap so it will not mess-up the drain of the bell syphon. I have been finding that two 45 degree fittings to turn a 90 degree turn will make for a better flow inside the pipe making your pump not work so hard. This is what I have come with, I may be off but this is the fun part of the system. Our mistakes are the true learning benefits of life. Good luck and dive in and play plumber.
PS draw a map of what you want to do then think what it would do and try it don't glue the fittings and if it don't work take it apart and do over. Just have fun Tony