I think a better use for the sight glass is in the mash tun. I don't like to leave much water in there when the sparge is done and since I can't "see" the water level in the mash after if has gone under the grain level that is what I intend to use the site gauge for.
Brewing since 1989 - BJCP National Rank
Fermenting: McChouffe clone, Samiclaus clone
Conditioning: Belgian Tripel, Barrel Aged Baltic Porter - in sherry barrel, Belgain Easter Ale
On tap: CAP, Dortmunder Export, IIPA, Dubbel Chocolate Stout, Wee Heavy, Whiskey barrel aged Wee Heavy, Baltic Porter