This chapter explores the concept of squat tech as a way of problem solving in situations of infrastructural need and resource constraints. Squat tech should be understood as a sociomaterial assemblage, in which material agency, social setting and different knowledge become aligned to respond to a particular need. This alignment is a gradual, messy process, grounded in particular material conditions and the formation of different clusters of competence. It also applies these notions of competence, material agency and improvised learning to explore the sociomaterial assemblage of squat tech, using the example of the construction of a compost toilet in the eco-squat of Can Masdeu in Barcelona. It also need to consider urban constructions, including squat tech retrofit, as sociomaterial as well as fluid, and engage with the dynamics that bring them into being. Focusing on the conditions and dynamics of assembling squat tech solutions holds some interesting implications for the wider debates surrounding retrofit experiments and sustainability transitions.