Install a drain stopper so the stopper is removable.
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PF WaterWorks ClogFREE Never Clog Pop-Up Drain, Magnetic Stopper, Transparent ABS Body w/ Overflow, 1.6-2" Sink Hole, Chrome PF0324 - The Home Depot
plumbing - How to replace sink drain stopper - Home Improvement Stack Exchange
Bathroom Pop-up Stopper Replacement for Pop-up Drain Assemblies in Brushed Nickel - Danco
The Plumber's Choice 1-5/8 in. Bathroom Faucet Universal One Touch Vessel Vanity Sink Pop Up Drain Stopper Without Overflow, Polished Nickel 1301R - The Home Depot