Acrylics in the drain?
Yes, that concern is very valid, and it has always been a problem in any school art room I've ever been to (even though we used only water paints in school).
You should never wash big amounts of paint down the drain. The safer method is to simply let it dry and dispose of the remains in the household waste. Bigger amounts should be left to dry in a disposable container or plastic bag. Smaller amounts can be transferred to some old newspaper, paper towels, or similar disposable surface.
Brushes and mixing palettes should be wiped clean with a paper towel and then rinsed in fresh water. After you finished rinsing, continue letting the water flow for another minute to wash all the residue down your pipes. This is also useful for rinsing the pipes of old soap or fat residues (for example, after washing very oily dishes).
One solution I personally use: My mixing palette is a common glazed saucer. I let the paint that I no longer need dry on the saucer and then soak the whole saucer in water the next day. The acrylic paint won't dissolve in the water, but it will release from the glazed surface, and I can easily peel the paint remains from the saucer and dispose of them in the waste.