One form of sewer comprises a pipe having a bottom section 100 incorporating a flow channel 101 along which sewage flows. A cable guide 110 comprises a body section 111 and an arm section 112. The body comprises a panel 111 curved so as to be able to lie substantially flush with the walls of the flow channel 101 and the arm comprises a tube with an internal passage. The arm 112 projects from the body 111 and the passage within the arm 112 extends from an opening 113 provided in the body 111 to an opening 114 provided at the distal end of the arm 112. The openings 113, 114 and the passage within the arm 112 are of suitable dimensions to carry a cable 105. The body is also provided with a cable clip 115.