[Lee, Daniel]

Following up on this post, we evacuated the oven for 5.5 hours. The final pressure was still around 15 Torr. I turned the oven off, but this time I closed the valve to the pump. After 18 hours, the oven pressure did not go up by more than 1 Torr. This means there is a leak upstream of the valve to the pump. I think is it the connection from the tubing to the oven itself. Other possibilities are the connection from the tubing to the pump (unlikely the dominant culprit as this connection is very tight), the KF O-ring seal (unlikely to leak this much), the pump itself, the tubing itself, or the oven between the valve when it is open and the tubing.