Abstract: A lapping compound holding tank (60) positionable at least partially below the lapping chamber of a lapping machine. The cylindrical tank is rotatable about its axis and includes a fixed mixer and scraping assembly (80) positioned in the tank. The mixer and scraping assembly provides strong small-scale turbulence or even scraping action very close to the bottom (64) of the tank. The tank configuration enables efficient use of floor space since the tank occupies much of the same area as the lapping chamber of the machine. There are fewer potential accumulation surfaces between the lapping chamber drain and the tank. Cost and complexity of the tank is reduced. The present invention also includes an in-line compound filtration system (120) comprising an inlet section (122), a funnel portion (128) having a tubular portion (130) and an outlet (132), and a removable magnetic unit (134) having a cylindrical magnet (136).