A fluid processing system is described having at least two chambers. Each of said chambers is separated in a first and a second part by a flexible membrane, the first part, in use, comprising essentially a gas and the second part, in use comprising essentially a non- gaseous fluid, an inlet and/or an outlet means. One or more channels are provided connecting said second parts of said at least two chambers, wherein at least one of said one or more channels includes a pressure sensitive one-way valve. Further, means for exerting pressure on said first part of at least one of said at least two chambers is provided to allow transfer of a sample liquid.