Drain pan keeps filling and shutting air off

This happens a couple times a year. We shop vac the water from the pan, pour some vinegar down the pipe then suck the gunk out the other end with the shop vac. This time it’s happening every 24 hours or so. My husband heard we should use Drano (or similar) to really break up whatever is stuck in there. Would that work? It’s probably calcium from hard water. We’re in Florida and this is in the garage; so very humid. I included video of the water pouring out as soon as it stops running (reaches our set temp of 76) and I circled where we pour the vinegar. Our drain pan is very rusted from constant condensation. Any other suggestions?