Here's an option to keep the drain line clean, especially if you're not around to do the monthly hot water flush.
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Some microbiology geeking out:. The snot like slime in an HVAC system, is a biofilm (Zoogloea) that forms from a combination of dust, moisture, and microorganisms.
This was not a problem when the coils were copper since that material inhibits microbial growth. Copper is effective at very low concentrations.
Some options for adding copper to a system discussed here:
https://youtu.be/5VOffWjmWkk
Copper sulfate is often used in tablets or crystals placed in the drain pan but they only last a few months.
To avoid opening up the system, 1 oz of copper sulfate (fungicide) can be added to the drain after monthly flushing as a preventative to help deactivate/prevent any remaining mold in the drain line.
https://a.co/d/aGPNbrg