my grow box is at back of garage where 2 neighbours gardens are in contact with it and was blowing air out towards them and other day got lots of strong smells which i need to sort before door goes in round me.made a diy carbon filter earlier but dont think its goin to work.used a unused sewer pipe 220mm diameter with a 7" desk fan forcing air up through it with a flower pot on top filled with carbon held in by tights.cant feel any air coming through and was wondering if i needed a more powerful fan or does the air seep through it without u really seeing it.dont no as never seen 1 in operation, all help appreciated