Ama-Drainer 301C Pump: A Surprisingly Simple Fix My Ama-Drainer 301C pump is installed in a KSB Box Mini—probably the kit your plumber installs for washing machines or small sinks that sit below the household waste line. Normally, you’d think this thing has an easy life… until it doesn’t. After my sump overflowed three times, I had cleaned the pump it worked after a good clean everytime, I finally called the plumber in the hope to use my building warranty to have it replaced.