Exemplary embodiments are directed to a system for sampling sub-slab soil gas having an adaptor body that includes a first barbed portion, a collar portion, a second barbed portion, an internal cavity that axially passes through the length of the adaptor body, and a coupling portion. The system further includes one or more extensions such as a fitting extension, a filter extension, a sieve extension and a length extension, each of which are threadably retainable with the coupling portion of the adaptor body.