Cistern overflow draught eliminator

We have an old toilet cistern in one of our bathrooms that the wind howls through during the winter, chilling the room significantly and also presents a risk to the cistern freezing up. This dip end fits to the top of the pipe (For bottom entry overflows) and dips into the water which prevents the draught through the pipe. The pipe will still allow water to overflow through it should the ballcock begin to fail.
Most modern cisterns overflow into the toilet pan but if you have an older design