One drawback of the grainfather is that you can't easily monitor gravity, pH etc of the sparge runnings going into the kettle. With a 3V system you can measure these things as the runnings are coming out of the mash tun. There are reasons why a brewer might want to control how much sparge runnings are collected. One might want to maximise efficiency or stop sparging once runnings reach a low enough gravity. More generally it puts the brewer more in control of the process rather than just hoping and assuming that the amount of sparge runnings collected is appropriate for a particular brew.
You could put a collection plate between the malt pipe and grainfather boiler, with a tap on the side and a hose running into the main body. You could also add a second smaller tap to take readings for a refractometer or pH meter. I have done a rough sketch in MS paint to illustrate the idea.
I wonder how much it would cost to get something like this made up? It wouldn't necessarily need to be cylindrical. You could use a rectangular or square collection plate as long as the length and width dimensions were more than twice the radius of the grainfather opening. I am thinking I might even be able to modify a really big drip tray to do this.
