We, just bought a house and noticed a strange plastic pipe line going upfrom the laundry sink to the upstairs shower. When you run a bath there is no problem when you turn the shower on not all the water goes to the shower head some goes through this pipe and down into the laundry sink and runs down that drain.this is a terrible waste of water let alone hot water.why is it there and what can we do to fix it.this is a half duplex and over 30 years old