In the original post you said that you want to wait until you have several prints "... to save Selenium". The diluted selenium toner is not discarded after use. Store it and continue using it as long as at still works. It will slow down as it gets older and may have some black particulate but, as long as it still tones, it is good. Selenium is one of the materials you don't want to be pouring down the drain any more than is necessary.