I don't think you can store soiled water for too long. And considering its only an ounce its like throuwing away 30 cents or whatever. If you must recycle I would let it sit for a while and then scoop out water nearer the top and fill a few spray bottles with it to be used on your wheels and rockers, bumpers. The areas that get really dirty frequently.
I only drive my BoxsterS a few times a week (public transportation daily) but before each drive
I will spray and wipe the wheels, clean all the glass, dress teh tires with Michelin, shake out the red carpets and hit everything inside and out (except paint panels) with FK 425. Takes five minutes and the car look like was just washed.