Waterra Vapour Sampling EcoPlug. This specialized well cap uses a stainless steel valve which allows you to extract a sample of the trapped headspace vapours. Pressure tested to 20 PSI, these well caps prevent the loss of well gasses to the atmosphere. The Sample Port Adapter allows you to extract the sample without removing the cap from the well. The Sample Port Adapter can be attached to a perstaltic pump in order to draw out even more of the trapped headspace gasses.