Washing the brushes in sinks will *eventually* clog drains, not straight away! A few times (or very small amounts like artists are using) is not really an issue with normal pipes. You can clean your brush under the tap outside if it's water based, or here it's recommended to do what you say - rinse off, wait for water to evaporate or soak with kitty litter or newspaper, wrap up and throw out remaining paint.