In the documentation it says

The field is determined by a Scalar Field DOP connected to the second input. The scalar field is interpreted as a signed distance field. One approach is to use a Fetch Data DOP to copy the surface field of a fluid simulation].

https://www.sidefx.com/docs/houdini/nodes/dop/buoyancyforce [sidefx.com]

The problem I am having is with ‘copy the surface field of a fluid simulation’.

In a simple FLIP tank sim how is this accomplished? Can anyone post a bare bones .hip?