Control Odor from Air Conditioner Drip Pan

One of my evaporator drip pans gets "stagnant" and produces an odor into the guest stateroom when the A/C fan is running. It drains well, but a small amount of water always remains in the pan. I have used Pine Sol, etc to flush the pan but the odor always returns in a few days. I hesitate to use bleach to kill the odor as the pan drains into a sump and I don't want to damage the workings there.
I did a quick search and could not find a solution on this site. Any suggestions? Thanks

Many pans don't drain well. Look at changing the level of the pan mount to direct water to the drain or look at moving the drain.

Bleach will work and I don't see much harm to the sump. But if you want to try something a bit safer and will produce no chlorine odor, try a bottle of hydrogen peroxide.

First plug up the drain hole so that you can maintain a level in the pan. Then dump in the peroxide and enough water to get the level comfortably as high as it ever goes. Let it sit for a few hours then remove the plug and drain. Maybe scrub any loose slime and rinse.

This treatment is kind of like bleaching the hot water tank and piping to kill the hydrogen sulfide odor. You kill the bacteria that makes the odor, it works for a while, but the bacteria returns.

But if you completely kill the bacteria with the peroxide, it should last for a month or so.

David

David's comment got me wondering if the smell is coming from the sump not the pan.

Yeah check the sump.

These work well at controlling the gunk in a pan.

Pan-Treat

Yes, already eliminated sump and waste tank filter as culprits, it is definitely the drip pan. The hydrogen peroxide or Pan Treat appear to be the answer I was seeking, thanks!