probably need to pause?

gistfile1.js

from = require('from')
through = require('through')
concat = require('concat-stream')

from([1,2,3,4,5])
.pipe(through(function(data) {
  setTimeout(function(){
    console.log('pushing data', data)
    this.push(data)
  }.bind(this), 300)
})).pipe(through(function(data) {
  console.log('pushing data second time', data);
  this.push(data)
})).pipe(concat(function(result) {
  console.log("voila", result)
}))

output:

voila undefined
pushing data 1
pushing data 2
pushing data 3
pushing data 4
pushing data 5