Good morning, First when ...

Good morning,

First when you say grey water, you are talking about water from other sources in a household excluding toilet waste? Washing machines, sinks, and showers?

There should be some type of bar screen, grit removal, primary clarification, or other types of pretreatment.

What would be the discharge of this water? This would dictate the treatment post sand filter.

You would definitely need to remove plastics, grit, and heavy materials.

Sand filters are for removing suspended solids only.

Hope this helps!