You need a Flow
:
import akka.stream.OverflowStrategy.fail
import akka.stream.scaladsl.Source
import akka.stream.scaladsl.{Sink, Flow}
case class Weather(zip : String, temp : Double, raining : Boolean)
val weatherSource = Source.actorRef[Weather](Int.MaxValue, fail)
val sunnySource = weatherSource.filter(!_.raining)
val ref = Flow[Weather]
.to(Sink.ignore)
.runWith(sunnySource)
ref ! Weather("02139", 32.0, true)
Remember this is all experimental and may change!