A U-tube arrangement for monitoring, observing, or measuring gas flow or gas generation of in a closed system can include a U-tube having a first arm, a second arm, and a bridge connecting the first arm to the second arm; a liquid disposed in the U-tube; an attachment conduit for coupling to the closed system and in fluid communication with the first arm of the U-tube and the closed system; a first valve for controlling fluid flow between the first arm of the U-tube and the closed system; an external conduit in fluid communication with the second arm of the U-tube and either an external atmosphere or external pressure source; and liquid level sensors disposed along at least one of the first arm or the second arm.