A non-return valve having a circumferential face and a channel with a mouth at one end of the channel and located in a groove having circumferential edges which are adjustable and fixable relative to each other and a valve comprising a O-ring manufactured of an elastic material for releasing the mouth at a predetermined pressure in the channel. Sufficient difference in voltage is applied between the liquid and the collecting electrode for a corona effect between the drop of liquid at the end of the capillary tube and the collecting electrode and the spraying of the drop by electrospray. The inner element is disposable in a toilet and the outer element is disposable as solid refuse. Thus, powerful and intuitive correction of wind direction readings is possible.