Are they the tank type or one piece? They began in the late 60's and were still being made in the mid 90's. I assume they were discontinued when 1.6 gpf became the standard since they used water continuously when the Vent-Away feature was activated. They cost about $200.00 more than the non vented model. If you are asking what their value is today, it would be zero. It was a complex addition to the toilet and I have never met anyone who had one that actually knew how to use it. Most users assumed it operated automatically everytime the toilet was flushed. It didn't.