Is an improper water heater exhaust pipe slope dangerous?

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   getting a shorter water heater
2. 2
   finding a higher spot on the chimney
3. 3
   Turning off the heater
4. 4
   Removing damaged duct tape and cutting away compromised drywall
5. 5
   Hiring an HVAC contractor to inspect and replace the venting system

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.