I use boiling hot water with bleach on my drain. Additionally, I use my shop vac to suck any gunk that has developed inside the pipe. This can ruin a system. Make sure it gets fixed.

Bleach combined with a significant amount of HOT WATER

Since the drain line flows fine, I would look at the condensate pan itself next. They crack or rust through and drip straight to the floor even with a clear line. Also check that the unit is sitting level and look at the evap coil for icing when you get the cover off.

I wouldn't conclude the drain line "flows fine" based on the OP's statement of how they checked it. The vertical portion of the drain line may be clear, but there's no way to know the state of the horizontal portion of the drain line without removing a panel and visually inspecting it. Ditto for the ability to clean it.

Since the drain line flows when you pour water in, I would check the next few places in order before assuming the line is clear. Look at the condensate pan for a crack, rust, or standing water, and check that the unit is level so water is actually reaching the drain outlet. When you take the cover off, also check the coil for ice and a dirty filter, since restricted airflow can cause icing and then a drip when it melts. If the pan and coil look fine, the horizontal section of the drain can still hold debris even if the vertical part flows, so it is worth inspecting that section and clearing it from the unit end. If you find the pan damaged or the coil icing repeatedly, that is a good point to stop and have a technician look at it rather than keep running it.

That is a common problem in humid weather, and a drain that accepts poured water does not always prove the system is draining properly while it is running.

The most likely causes are a partly blocked or poorly sloped condensate line, a cracked or rusted drain pan, a disconnected or loose joint, or restricted airflow causing the coil to ice up and then drip as it melts. Condensation can also form on cold ductwork or fittings when warm, humid air reaches them, which can look like a leak at the unit itself.

A few things you can safely check: first, turn the system off if water is near any wiring or electrical parts. Check the air filter and replace it if it is dirty, because restricted airflow is a frequent cause of freezing. Look for standing water in the pan, a visible crack, or a joint that has worked loose, and watch the outside drain while the system is running to see whether it is dripping steadily. Keep the area dry and do not remove sealed panels, touch refrigerant lines, or work on live electrical parts.

I run Ocala Pro AC Repair here in Ocala, FL — we see this a lot in Florida heat.

Call a professional if the dripping continues, the pan is damaged, the coil keeps freezing, the drain keeps blocking, or you notice a musty smell, damp insulation, or water spreading to ceilings or floors. Those signs usually mean the fault is inside the unit or in the drain arrangement, and it is worth having it checked before it causes more water damage.