This tool enables the parameters on the Viscosity tab on the FLIP Fluid Solver.
Viscosity is the thickness and resistance to flow of the particle fluid. A fluid with higher viscosity tends to flow more slowly and appear thicker than one with low viscosity. For example, a substance like honey has high viscosity, whereas a fluid like water has low viscosity.
Using Make Viscous
Create a FLIP Fluid Object.
Click the Make Viscous tool on the Particle Fluids shelf tab.
Select the FLIP Fluid Object to add viscosity to, and press Enter to confirm your selection.
By default, the Viscosity Scale on the FLIP Fluid Solver is set to 1. You can use the slider on the Viscosity tab to adjust the amount of viscosity. This parameter is a scale applied to the Viscosity field after applying the attribute effect, which is useful for adjusting the global amount of viscosity.
There is also a Viscosity parameter on the Physical tab of the FLIP Object that you can modify if you want a specific fluid object to have different viscosity.
For more information, see the Viscosity help page.