You mens something like this ...
Published by Peter Dew, Senior Policy Officer at Office of the Great Barrier Reef - EHP
You mens something like this or you want plumbed in solution?
https://www.thomassci.com/scientific-supplies/Adjustable-Volume-Dispenser
plumbed in solution
https://bd.dosatron.com/Solutions/WaterLine/Catalogue_Catalog/DOCATEAUEN.pdf