If the requirement is sampling from an enclosed pipe then it is more sensible to use a properly designed In-line Sample Acquisition System.
The SIRIS Guillotine Sampler is an extremely robust and reliable in-line sampler, and built on the same module as the MCERTS approved Efconomy vacuum sampler. The unit is specifically designed for In-line, closed pipe sampling applications and is not simply a modified Vacuum sampler. The system drives directly into the pipeline's flow and takes a 50ml sample shot.
The sampler can operate on a flow proportional basis being triggered by an associated flow meter such as Electromagnetic type and can be specified in a range of options.