What is the recommended height for a standpipe in relation to the trap weir?

The recommended height for a standpipe in relation to the trap weir is between 18 to 42 inches. This height range is established to ensure that the standpipe is adequately positioned to prevent issues like siphoning, which can occur if the vertical distance is too low. A properly installed standpipe helps maintain the necessary trap seal and allows for effective drainage while also preventing backflow and ensuring a snug connection to the drainage system. Proper height alignment within this range helps facilitate effective drainage and mitigates the risk of plumbing issues that can arise if the height is not maintained correctly.