To calculate rainwater discharge systems, we use our own program with which we can calculate the right size of the pipes for every special situation.
We always advise to use a bigger diameter at the beginning of the stable to limit the resistance alongside the stable as much as possible. With this the diameter of the pipe to the ditch can be as small as possible and also the risk of overflow at the beginning of the pipe is as little as possible.
When the pipes of a rainwater discharge system need to be hanged, we advise to use brackets instead of straps. When using brackets, the pipe is hanged free from the wall. This way sand/soil can get between the pipe and the wall, which limits the risk of the pipe dropping down at a later time.