A drainage channel should be placed so that water flows away from the building. The channel should be sloped so that water flows quickly and easily to the outlet. The channel should never discharge water onto the property of another person.

It depends on the context. If you're asking about a drainage channel for water, then you need to place it somewhere where the water will flow away from the structure or area that you are trying to protect. If you're asking about a drainage channel for air, then you need to place it somewhere where the air will flow away from the structure or area that you are trying to protect. Thanks for reading! If you have any other questions, please let me know!