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
Member of KROC and Foam on the Range
Fermenting: Imperial IPA, Belgian Blonde
Conditioning: Dortmunder Export, English Barleywine
On tap: CAP, Steam Beer, ESB, Honey Doppel Mai-Bock
Newly Bottled:Belgian Tripel, Belgian Easter Ale, Summer Saison