Cork is not considered to be dishwasher safe and can be ruined if put in the dishwasher.
It's best to not put cork in the dishwasher and instead wash the cork by hand.
Cork is absorbent material and will absorb the water and possibly swell up in the dishwasher and crack or break apart.
So you should just swish them around in the sink with some soap and water and then wipe them off by hand.
You don't want to leave the cork in the water for longer than a few seconds though because it will then swell up which has happened to me.
Just run a bit of water over them after you dip them in soapy water and then the water will rinse the soap off.
Or dampen a washcloth and wipe the cork material clean.