I agree that it'd be better not to buy synthetics as they stand, but that requires manufacturers to shift their production to natural fibers. I think regulation / remediation sounds like a good way to encourage that shift. Consumers buy what's on offer - if everything in the market was natural fiber, consumers would choose accordingly, otherwise they are likely to choose whatever meets their needs (which maybe low-price, or high-fashion, but without more education and alternatives, won't be cleaner water).

Which synthetics? Does that include polyester? Rayon?

No. Under capitalism, companies make what their consumers can afford. And these days, very few consumers can afford what they want, so the market becomes irrational. We have to buy, and thus encourage production of, what we don't want... because it's all we can afford.

The problem here is synthetics are generally considerably less resource intense than natural fibers, I looked into cotton vs polyester a couple of years ago https://www.ryanmercer.com/ryansthoughts/2016/7/19/environme...

While the synthetics and artificial fibers are bad as they pollute the environment downstream, cotton production requires roughly 20,000 liters to produce 1kg of fiber while polyester requires SEVENTEEN liters of water.

> Vote to pass legislation that taxes synthetics

Just regulate the items you don't want with rules. If you want it gradual, make the rules gradual. No need to build more money-collecting bureaucracy and keep asking people to pretend the gatekeepers/spenders are trustworthy.