A thermoplastic chamber for leaching wastewater or other use, which is designed so that when jointed to a like chamber the horizontal plane angle between the chambers can be adjusted, has one or more stops which can be selectively used to prevent rotation, for instance, to make the joined-together chambers lie along a straight line. Preferably, the stop is integral part of the chamber base flange; and it hinges and bends upwardly when moved to its working position, so the stop engages and limits movement of the end of the mating chamber.