Plumbing my garage for compressed air...

Pitch them all back torward the compressor . This way the horizontals lines will drain back to the tank . Less build up in the verticals. I used galvanized wish I would have use copper on the long runs. I already see brown water at the drains on the drops. Put a automatic drain on the tank. Everytime my compressor stops it drains the water off itself. They are cheap @ Harbor Freight