Can I use the other brand of rinse in the top tank & BioMagic concentrate in the waste tank
No. Any chemicals will interfere with the way the bacteria work. Just empty the old product out by draining it or pumping through, rinse again with fresh water, then re-fill with fresh water. It is not necessary to use any product in the top tank except fresh water. If you would like a perfume or nice smell in the top tank we can supply extra organic perfume or you may use a small amount of essentail oils.( not Eucalyptus or Pine)