Mid century modern bathroom vanity – Sinks work perfectly and pots. They have a drain so that water will not rot the roots of the plant. Since most sinks are ceramic, they are quite weather resistant as well. You want to put a plant in the sink with a shallow root system, such as petunias, morning glories, and lilies of the valley. Check with your local nursery about what plants they have a shallow-based pot.
Mid century modern bathroom vanity, to use the vanity for storage, wears out pipes. These guts just get in the way. Once you have removed the pipes, but you want to seal up the holes in the wood of vanity, like the hole in the sink to prevent your clothes, or whatever you can store, from a mal seizures. Seal the wood holes with either a thin small plate made of balsa wood nailed over the hole; plaster; or tape. Since the holes are behind the vanity where no one sees them, what you seal the hole does not matter as long as it prevents bugs and moisture from getting into the vanity.
The mid century modern bathroom vanity also functions as a kitchen countertop space. Just to the sink will not pass water does not mean it is not useful. Use the drive vanity to chop food and the sink to keep the vegetables or fruits. Keeping healthy foods out encourages you to eat them.