a filtration vessel at least partially removes a contaminant from a fluid . the vessel has an inlet pipe which is mounted to a first end cab and to a supporting plate of the vessel . the inlet pipe has at least one slot through which the fluid is injectable into an inner volume of a vessel body . at least one membrane rod including a plurality of membrane straws is mounted to the first through hole of the supporting plate such that the membrane rod extends from the supporting plate into the inner volume . a method for backwashing the device includes injecting gas in the storage volume and a method of detection of leaks uses gas bubbles .