I don't bother to mix it. Just pour it into a bucket with your pvc, boo, whatever and fill it with water. When it quits sucking in the water, you're good.
Actually, IMHO doing it backwards is best! I put 2+ gallons of water in a bucket and then slowly pour secrete into the water. If you want concrete up to a certain level' ion the bucket you can drill holes in the bucket at the level you wish. The Sacrete will displace the excess water and once you've poured Sacrete in To displace water at the level that you drilled the holes, stop and arranger your "boo or Willow or whatever, then allow the concrete to set up.