An assembly comprising: a gas turbine engine comprising: a fan section delivering air into a main compressor section, said main compressor section compressing air and delivering air into a combustion section, products of combustion passing from said combustion section over a turbine section to drive said fan section and main compressor section wherein a gearbox is driven by said turbine section to drive said fan section; and an environmental control system including a higher pressure tap at a higher pressure location in the main compressor section, and a lower pressure tap at a lower pressure location, said lower pressure location being at a lower pressure than said higher pressure location, said lower pressure tap communicating to a first passage leading to a downstream outlet, and having a second passage leading into a compressor section of a turbocompressor, said higher pressure tap leading into a turbine section of said turbocompressor such that air in said higher pressure tap drives said turbine section to in turn drive said compressor section of said turbocompressor, and a combined outlet of said compressor section and said turbine section of said turbocompressor intermixing airflow from said first passage, said compressor section, and said turbine section of said turbocompressor, and passing the airflow downstream to be delivered to an aircraft use; and a pylon supporting the engine, characterised in that: the pylon defines a lowermost surface and the higher pressure tap extends above a plane including the lowermost surface; and the higher pressure tap comprises a double wall tube above the plane for preventing leakage from impinging on a portion of the pylon. a gas turbine engine comprising: a fan section delivering air into a main compressor section, said main compressor section compressing air and delivering air into a combustion section, products of combustion passing from said combustion section over a turbine section to drive said fan section and main compressor section wherein a gearbox is driven by said turbine section to drive said fan section; and an environmental control system including a higher pressure tap at a higher pressure location in the main compressor section, and a lower pressure tap at a lower pressure location, said lower pressure location being at a lower pressure than said higher pressure location, said lower pressure tap communicating to a first passage leading to a downstream outlet, and having a second passage leading into a compressor section of a turbocompressor, said higher pressure tap leading into a turbine section of said turbocompressor such that air in said higher pressure tap drives said turbine section to in turn drive said compressor section of said turbocompressor, and a combined outlet of said compressor section and said turbine section of said turbocompressor intermixing airflow from said first passage, said compressor section, and said turbine section of said turbocompressor, and passing the airflow downstream to be delivered to an aircraft use; and a fan section delivering air into a main compressor section, said main compressor section compressing air and delivering air into a combustion section, products of combustion passing from said combustion section over a turbine section to drive said fan section and main compressor section wherein a gearbox is driven by said turbine section to drive said fan section; and an environmental control system including a higher pressure tap at a higher pressure location in the main compressor section, and a lower pressure tap at a lower pressure location, said lower pressure location being at a lower pressure than said higher pressure location, said lower pressure tap communicating to a first passage leading to a downstream outlet, and having a second passage leading into a compressor section of a turbocompressor, said higher pressure tap leading into a turbine section of said turbocompressor such that air in said higher pressure tap drives said turbine section to in turn drive said compressor section of said turbocompressor, and a combined outlet of said compressor section and said turbine section of said turbocompressor intermixing airflow from said first passage, said compressor section, and said turbine section of said turbocompressor, and passing the airflow downstream to be delivered to an aircraft use; and a pylon supporting the engine, characterised in that: the pylon defines a lowermost surface and the higher pressure tap extends above a plane including the lowermost surface; and the higher pressure tap comprises a double wall tube above the plane for preventing leakage from impinging on a portion of the pylon. the pylon defines a lowermost surface and the higher pressure tap extends above a plane including the lowermost surface; and the higher pressure tap comprises a double wall tube above the plane for preventing leakage from impinging on a portion of the pylon.