The Lavatory Museum is a collection of six immersive art exhibits and the biggest “clean” ball pit on the planet.
It is an hour-long experience, 20 minutes of which is in the Pit.
A Mega Drop, on the other hand, is 100K+ plus balls dropping from above and requires a separate ticket usually on a different day. It is in the Pit, lasts an hour and does not include a visit to the Lavatory Museum.
See website for more details.