I would vacuum out the outlet where it terminates outdoors or Back-flush with a garden hose from outside.

My theory on bleach or vinegar is the vapor, along with any fresh painting of walls, new carpets, sofa etc. tightening up the residence over the years is outgassing increases to where it has the potential of increasing the possibility of indoor coil leaks… Just my theory though…..

My friend lives in a new community in Florida with super tight residences, all new everything, floors, paint, carpets, then the HO, typically buys new furniture and Contractors tell these HO to add bleach or vinegar in the vent line on the condensation drain line practically monthly. He see many residence having indoor coils changed in only a few short years. His neighbor unit, lasted two years.

Tranes and Lennox are in his Community.

 

Proper slope
Proper supports
Clean out where needed

 

.
Downflow in the attic is a tough issue because maximizing slope gives best drainage. Can you post a picture from 8 to 10 feet away?
..

 

Enclosing the picture.
The primary drain works very well at this time. I am looking to keep it that way for future.

 

I 2nd and 3rd the "add proper slope" so there is no stagnant water in drain line.

I would avoid chemicals due to the unintended consequences.

Instead, use a wet vac on the outlet of the drain. If you don't have a wet vac, you can pick up an inexpensive one at your local hardware store.

 

Is this one of those that has a long low spot under the slab that collects water?

 

Where does it go from there?

 

It runs on the attic floor as shown in the picture and through the external wall ( the pipe is hidden as it was installed when the home was built ) , it goes down one floor to come out in the side yard.
I do clean this drain periodically using a powerful wet vacuum connected to that outlet, but also looking at additional insurance by using vinegar once in a while. I am in Bay Area, CA and the AC hardly runs for few weeks a year, 4-6 hrs a day.

 

Is there a trap somewhere in this line, just not pictured?

Somebody handy could easily install a clean out port in the shown drain set up and if need be, get the proper slope in the pipe.

 

.
No doubt what's pictured could easily be improved. And work.
..

 

We need to see a lot more.

 

Water and elbow grease are the two best cleaners.
Some people recommend vinegar but I don't because I've never found it to work for that type of grime.
I would recommend you as a homeowner just use a Shop-Vac to suck out the drain from the end once or twice a year.
If you have issues with it clogging regularly the drain most likely needs to be re-plumbed to fix the cause.

 

I don't think I've ever seen a condensate drain line on an A/C with slime in it, certainly not plug due to slime in there. Plug from filth (dirt in the air), yes.

On the other hand, refrigeration equipment, particularly walk in coolers, yes. Weird how some would have severe problems, often plugging up 3-4 times a year, while others never had an issue. I could never figure out why, except it must have been environmental.

Which leads me to believe if slime is developing in a residential A/C, it must be something environmental, either within the home or from the outside air.

 

It's very common in humid climates.

 

Trap per the mfg installation instructions

per post, verify pitch, & cleanout per IM

 

My customers had me do the yearly cleanout/flush out/ checkout and I have never or verrrrrry close to never had drain line problems. I got to re-pipe a whole bunch of 'not done quite right' drain lines.
I also have had a handful of customers that did their own drain line yearly PM because they liked to do their own work. I showed them how I do it and they were then 'qualified' to be a 'drain cleaner outer guy'.

 

definitely slope to keep water from staying in the pipe and growing gunk. I've started using slow release tablets to treat problematic systems.

 

Over the decades I have only seen a dozen or so horizontal drains w/ a T with the opening on the vertical w. a 3,4,6 '' stub. But, over the decades I have put in HUNDREDS of air vents in the horizontal runs.