How is life at the urban margins made and remade? In this paper, we examine this question in relation to ‘sanitation urbanism’, and through attention to what we call ‘infra-making’, defined as the interstitial labour of human and non-human agencies and atmospheres that take place in the production of forms of sanitation. We do so through close engagement to sanitation at the margins of two very different cities across the global North–South divide: Turin and Mumbai. Despite the apparent impossibility of comparing such different cities, in the paper we develop a form of ‘experimental comparison’ that is oriented at understanding the everyday making of specific urban processes around urban sanitation. We argue that a comparative focus on how urban life at the margins is made and remade is important for critical urbanism. Our experimental comparison leads us to a discussion of the relationship between specification and generalisation, in which the latter is positioned not as an end-point but as an informant serving to enlighten understanding and intervention in specific contexts.