Improve ventilation in your tank or toilet without letting mosquitoes and other vermin in with a Rain Harvesting Vent Cowl. Some tanks – especially those with inlet pipes that are plumbed directly rather than pouring through a tank screen – need help with ventilation. Vent Cowls can be glued directly to the vent on top of your tank in order to let your tank “breathe” and protect your rainwater quality. The Vent Cowl includes a mosquito-proof 955 micron stainless-steel screen to ensure that while air can get into your tank, mosquitoes and other vermin cannot.