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: Saison Autome, Cherry Mead
Conditioning: Dortmunder Export, Belgian Dubbel, O-fest, Vienna Lager
On tap: CAP, Cider, Impy Cherry Stout, Rye Dunkel Bock, Belgian Chocolate Stout, Hopslam! Clone
Newly Bottled: Belgian Blonde, Belgian Quad