The chemical composition of interstitial waters of modern sediments must be known for a greater understanding of early diagenetic changes. In order to get an accurate idea of the chemical composition a method for extraction must be practical, adaptable to shipboard use, and avoid leaching or evaporation. A modified filter press was built of stainless steel, in which a piston, either manually or gas-driven, expresses water from a cake of sediment through a filter paper backed by a stainless steel screen and a solid steel plate drilled with many holes. The bottom of the squeezer is a shallow funnel that delivers the sample directly to the storage bottle. The squeezer is adaptable for use with inert atmospheres such as Ar.