Just pop out the plug covering the drain

Should be at the bottom right inset below the round knockout.

The right opening has a round cover in the bottom. Can you pull it up with the plastic stalk? Maybe with pliers?

Maybe they covered the hole up so sewer gases don’t go into the house.

Yes. What everyone else said. Pull out the cover and that's the drain. Make sure you secure the drain hose to something. They tend to kick themselves out if the are not secured to something.

Are you sure the opening on the right is a blank? It looks like there is a cover that should pop off where the drain hose will go

Bottom right looks like the dryer vent. The drain is the cutout next to the hot/cold lines. Looks like a plug there

Right side is a knockout.

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