That's the size I buy every couple of years from the Chemistry Store. It keeps well in the sealed plastic bag in a dry basement, but I also pour it into empty plastic drums from Sears detergent. Phosphates used to be mined in Florida and elsewhere domestically, but that's played out so now it comes from China.
Mark WP Duet, if you do not have a membership that allows you to use the search feature in any forum, do a Google Search for suds saver. If you can use the Searcholator feature, try searching suds saver in the Imperial Forum. The feature answered a need for coping with the increased water consumption of early top loaders and was popular among former users of wringer washers who knew how to add detergent with each additional load to keep up the cleaning power of the wash water and generally had set tubs to store the wash water. The biggest sacrifice with using a suds saving feature with an automatic was keeping the water hot between loads during the spin, rinse and final spin of the preceding cycle. The possible trade off was the slanted end of the suds return hose which allowed the bottom inch of water with the settled dirt to stay in the tub after the rest was sucked back into the washer for the next load. That last inch was sent down the drain when the plug was pulled.
Saving suds is a great way to save hot water with a top loader, but it is much more fun if you have more than one washer and just drain the wash water into the next machine.