All of the symbols in RainCAD/EcoCAD are located in the \symbols directory. The symbols are then broken down into multiple subdirectories. Sprinkler symbols are located in the \symbols\sprinklers directory while plant symbols are located in the \symbols\plants directory.
All symbols must have a number for the file name. The file name cannot consist of any characters other than numbers. The largest value we can accept for a symbol number is 2,147,483,647.