I need to run 20 feet of 4 inch drain pipe horizontally along a concrete wall. Someone suggested saddle clamps and anchors. I am not sure exactly what type to use, especially if the pipe is full of rain water.
Any of the pipe hangers available at your local big-box home improvement store are designed to support a full pipe. They would be just decorations if they didn't...
Pick a type that seems simplest to you to use, get appropriate fasteners (you're attaching this to concrete, a simple screw or nail isn't going to do the trick), ensure you've got the proper 1/4" per foot of run slope (i.e. the drain end needs to be 5" lower than the input end after 20') and have at.
You can use J-hooks, saddle clamps, or just about anything else designed for the purpose.