Jamieson, Fausset and Brown on 1 Chronicles 26:16

16. the gate Shallecheth--probably the rubbish gate, through which all the accumulated filth and sweepings of the temple and its courts were poured out.

by the causeway of the going up--probably the ascending road which was cast up or raised from the deep valley between Mount Zion and Moriah, for the royal egress to the place of worship (2Ch 9:4).

ward against ward--Some refer these words to Shuppim and Hosah, whose duty it was to watch both the western gate and the gate Shallecheth, which was opposite, while others take it as a general statement applicable to all the guards, and intended to intimate that they were posted at regular distances from each other, or that they all mounted and relieved guard at the same time in uniform order.