How to Test a Condensate Drain Line Before Closing Drywall

A condensate drain line is small enough that people stop paying attention to it, but it can cause a nasty callback after drywall. I have seen a ceiling opened for what looked like an AC leak, and the actual issue was a drain line with a flat section that nobody tested before the wall was closed. The equipment worked fine. The water just had nowhere reliable to go. I check slope first, before talk…