A radar level gauge system for determining a filling level (L S) of a product in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation arrangement connected to said transceiver and arranged to propagate an electromagnetic transmit signal from said transceiver towards said product in the tank, and to return to said transceiver an electromagnetic surface reflection signal resulting from reflection of said electromagnetic transmit signal at a surface of said product; a reflector arrangement (8; 31) comprising: a pliable elongated member attached at an attachment location (24; 39) within said tank; a reflector member (22; 34) arranged along said pliable elongated member and spaced apart from said attachment location, said reflector member having a first maximum extension in a reflector plane; and a weight coupled to said reflector member (22; 34) in such a way that an orientation of said weight determines an orientation of said reflector member, said weight having a second maximum extension in a plane parallel to said reflector plane, said second maximum extension being smaller than said first maximum extension, wherein said reflector member (22; 34) is arranged to reflect said electromagnetic transmit signal back towards the transceiver as an electromagnetic reflector signal; and processing circuitry coupled to said transceiver and configured to determine a proof test level (L R) based on said transmit signal and said reflector signal, wherein said pliable elongated member is attached to said signal propagation arrangement, and wherein said attachment location (24; 39) is located at a periphery of said signal propagation arrangement. a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation arrangement connected to said transceiver and arranged to propagate an electromagnetic transmit signal from said transceiver towards said product in the tank, and to return to said transceiver an electromagnetic surface reflection signal resulting from reflection of said electromagnetic transmit signal at a surface of said product; a reflector arrangement (8; 31) comprising: a pliable elongated member attached at an attachment location (24; 39) within said tank; a reflector member (22; 34) arranged along said pliable elongated member and spaced apart from said attachment location, said reflector member having a first maximum extension in a reflector plane; and a weight coupled to said reflector member (22; 34) in such a way that an orientation of said weight determines an orientation of said reflector member, said weight having a second maximum extension in a plane parallel to said reflector plane, said second maximum extension being smaller than said first maximum extension, wherein said reflector member (22; 34) is arranged to reflect said electromagnetic transmit signal back towards the transceiver as an electromagnetic reflector signal; and a pliable elongated member attached at an attachment location (24; 39) within said tank; a reflector member (22; 34) arranged along said pliable elongated member and spaced apart from said attachment location, said reflector member having a first maximum extension in a reflector plane; and a weight coupled to said reflector member (22; 34) in such a way that an orientation of said weight determines an orientation of said reflector member, said weight having a second maximum extension in a plane parallel to said reflector plane, said second maximum extension being smaller than said first maximum extension, wherein said reflector member (22; 34) is arranged to reflect said electromagnetic transmit signal back towards the transceiver as an electromagnetic reflector signal; and processing circuitry coupled to said transceiver and configured to determine a proof test level (L R) based on said transmit signal and said reflector signal, wherein said pliable elongated member is attached to said signal propagation arrangement, and wherein said attachment location (24; 39) is located at a periphery of said signal propagation arrangement.