How often do I need to use the Twisters to prevent solids from building up?

That depends on the solids settling characteristic of the product….in some crudes, Twisters may need to be activated every other week to prevent BS&W buildup from causing operational problems downstream. In other cases, a client may choose to activate every two years, with the express intention of removing any bad actors from the system, through perhaps a 3-phase centrifuge.  And in other cases, a 10-year activation or more may be adequate.