I have an old castiron sink/drainboard combo that is about 42 inches wide. There is a mysterious 'third' hole in the sink right in front of the location of the current faucet. At first I thought maybe it was for a sprayer, but the location seems all wrong for that. I want to keep the sink and update its faucet. I would like to know what the third hole is for. It has a steel square shaped collar around it, and is about a 3/4" opening. I can't find a manufacturer name, but it was made in 1946. Thanks for any info!