Keep the system leak free.Sit at the extractor observe how the sap is coming in.On our sap ladder we had drilled a small hole in the bottom of the first star to let in air as it appeared that sap was not moving but sap coming in to the extractor started coming in sporaticaly.After more observation we concluded that sap flow kept coming in even when it appeared sap was not going up at the ladder.So why make a leak and reduce vac. level in front of 250 taps.