If I want to install a long (30ft+) drainage pipe underground for my sump discharge, should the pipe be perforated or solid? The pipe will flow down and out into a creek. This is in a region that has very cold winters (<0F).
If it can be guaranteed to have a continual and "definite" down slope to the exit point, perforated pipe is not necessary. If it is more of a flat run, or has sections where water will pool, holes are prudent especially in colder climates.
It is wise to remember that the ground moves during the winter months.. what was a slight down slope when you laid the pipe may turn into an up slope when the ground freezes.
Also, if you plan on running the pipe through an area that has trees close by, tree roots WILL find the holes in perforated pipe, and will eventually clog it.
Typical practice is to make the first 10 feet or so solid and use perforated after that, but that would vary depending on where it is relative to the building basement floor - for a pumped sump I assume the pipe is above the floor level, so 10 feet of solid to get it away from the building and then the remainder perforated to allow it to drain water from the yard as well.
If the pipe is below the basement floor level you would not need a pump, as gravity flow downhill from there would carry water away, and it would all be perforated.