A rocket engine with a manifold is in communication with a combustion chamber. A sense line extends through the propellant manifold and into the combustion chamber. The sense line includes a venturi arranged downstream from the combustion chamber, and at least one aperture fluidly connecting the propellant manifold to a sense-line passageway downstream from the venturi. A method of sensing conditions in a combustion chamber includes exposing an end of a sense line to the combustion chamber, creating a low static pressure in the sense line at a location upstream from the end, introducing a fluid at the location to purge the sense line, and sensing the conditions downstream from the location.