I run 24 oz. of water through my Keurig and pour that down the drain pipe. Have a receptacle on the other end to catch the water so you can be sure it's getting through.

Try a You Tube search.

I don't know what water temperature a Kuerig produces, but the highest recommended temperature for PVC pipe is 140 degrees. In another thread, some posters said that they used boiling water, which is not a good idea. You especially don't want to melt the glue that holds the piping together.

I was told by one serviceman to use water with vinegar, another told me to use a little dawn and water and another said not to use either as it could get sucked into the unit if it turned on during your water routine. I use hot water on the first of each month.

I do the same thing.

Have an AC service done every six months and you will not have this problem.

I use Sensible Air & Heat; He was just out a week ago. We were doing the vinegar, but he says 50% water 50% Bleach.

If you need a free funnel, cut the bottom off of any plastic bottle & the top becomes the bottom of your free funnel.

There doesn't seem to be any consensus on what to use (vinegar, dish soap, plain hot water, etc.), but very few technicians will recommend bleach because the fumes can back up into the air handler unit and cause corrosion.

Apparently this wasn't a problem when copper was used in the cooling coils. Copper is an antimicrobial even in very small concentrations

Some have suggested/claimed placing a few small copper rods in the drain pan helps keep the biofilm from forming.

We used to use it to keep algae from forming in our pondless waterfall.

Another suggestion in this thread:

Cleaning slime mold from condensate drains

I found some large 1" crystals of copper sulfate and put one in each drain pan.

The copper sulfate crystal very gradually dissolves in the condensate and keeps the drain and the pan completely clear of mold and slime.

I was doing this for my customers back 50 years ago when I owned a HVAC business, and continue to do it for my own condensate pans today.

You will never see mold growing on a roof below copper roof flashing. The same is true there.

Copper is a mineral and it's found in small quantities in the earth everywhere, so non-polluting. Most houses have copper plumbing with drinking water running through it. In high quantity, like the crystal, it would be dangerous if you ate it though.

FYI, I sent a message to the "Ask the Expert" section on the Munn's website about how to maintain the condensate drain line. This morning, they called me back and said that they no longer recommend using any chemicals to flush the drain. Their current recommendation is to add a gallon of warm water to the drain at least 4 times per year. This recommendation is endorsed by Carrier, which is a very common brand HVAC system in The Villages. In the past, Munn's recommended using vinegar, hydrogen peroxide, or dish soap, but they no longer recommend these chemicals.