i put one tablespoon of medora egg shampoo for hair in my washer bottle(considering that you are filling it from bone dry condition-i am using this as an example,never let yr bottle get bone dry,im jus telling you abt th ratio of shampoo to be added)
and put it in the windscreen washer bottle either with a small spoon or by means of some thin utensil,then i stir the water gently...
it keeps the windscreen amazingly clean..
dont use excess of shampoo as you will end up with white deposits around the nozzle of windscreen sprayer..
and NEVER use Detergent powder..it would scratch yr windscreen quite bad..
reduce th ratio of shampoo per one full washer bottle if u notice deposits around yr sprayer nozzle,personally i use medora hair shampoo and it does the job well

my desi/gharelo windscreen washing fluid 