We use a grantless system. I have used a grant as well, but not having helps with hot side airation. the system is a straight run out of the mash tun thru a valve, sight glass and then a valve. The First valve is kept shut which diverts the wort up an upside down U shaped pipe over the valve and back down to the other side of the first valve. It then travels thru the sight glass, the second valve and to the wort pump. On top of the U shaped pipe is a polypro "manometer" Essentially a translucent pipe that is taller than the hight of the mash bed in the tun. This allows us to monitor flow and draw on the bed. When we recirc, the wort is pumped from the mash tun up to a valve on the platform allowing the wort to cascade down on to the bed about 12" above. I have heard of some brewers using a plastic tube to bring the wort down gently on the surface to reduce airation. Hope that was clear and helps.
Jason Dunson Todd
Paper City Brewery