Qirbah is a vessel, commonly made from animal hide, used to transport water. Aqwām, plural of qawm, makes clear that the poet recalls loads belonging to people other than himself.
ʿIṣām is the strap for carrying the water-skin, and kāhil is the upper part of the back just below the neck. Dhalūl normally characterizes a compliant mount or trained bearer; here it conveys the speaker's willingness and endurance.
Muraḥḥal evokes the condition of repeated travel and loading. Rendering it only as “departing” would lose the important sense of experience and physical hardship within the line.