Abstract: A portal apparatus in the form of an arch-shaped pipe fitting (10) for use with a fumigation chamber that in part incorporates a flexible canopy. The pipe fitting (10) can be seated on the ground (12) so as to be positioned between the canopy and the ground (12). A sealing surface (22) on the pipe fitting (10) is contactable with the flexible canopy so as to provide a gas-tight seal. An assembly for directing the flow of gas in general, the assembly being operable in various configurations, and comprising first and second gas inlets and outlets respectively. An assembly for operatively coupling gas extraction, treatment and recirculation apparatus, and comprising first and second gas inlets and outlets respectively that can be selectively coupled in first and second configurations.