A package for an addressable array of multiple features carried on a first side of a substrate, and a method of using such package. The package includes a housing which receives the substrate such that the housing and received substrate define a chamber into which the multiple features face, and which chamber is accessible through a first port. The housing includes a first set of multiple fluid distribution channels each disposed between the first port and the multiple features of the received substrate so as to direct fluid flow between multiple different regions across the first side of the received substrate to or from the first port. The fluid distribution channels may be valved such as by being capillary sized or by being provided with a bubble formation device (such as a nucleating resistor). The channels can provide for an even flow of wash fluid across the array while confining sample to the region of the array.