A fluid sampling system for sampling the contents of a container of fluid includes an elongate hollow sampling conduit extending between a first end for withdrawing the fluid from the container and a second end for returning the fluid to the container, pump means for circulating the fluid between the container and the sampling conduit, a sample probe having a tip extending into the sampling conduit so as to contact the fluid within the sampling conduit, and a controller unit for controlling flow of the fluid within the sampling conduit and monitoring the properties of interest of the fluid within the sampling conduit via signals received from the sample probe. The present invention also provides an in-line pH probe.