My husband uses good old fashioned elbow grease and a scratch pad on our cast iron. For daily use, he is sure to set the wet pot back on the stove and heat it until it is completely dry. That's how we prevent normal rust from appearing on what we have. He seasons them with cooking oil on occasion, but, that's about it! Since we eat out of our cast iron, we don't use chemicals to clean or maintain it.

there shouldn't be a vent pipe on a sink it's a closed, pressurized system. I don't know what your looking at, more info would be nice.