I had a friend who did apartment cleanings and his secret trick to really bad soap scum was Coca Cola, he said store brands and Pepsi didn't work so well. Cover the drain, pour in a can and let sit for a bit and then it would just rinse away. That was back in the days of ceramic over cast iron, don't know how it might work on acrylic. But when I've had difficult ceramics (like little figurines that have collected grease and dust over the years) to clean I have had success in putting them in cola (I'm cheap and don't use name brand) overnight, and yep, just rinsing them off the next day.