Do you have to?
is it absolutley nessecary to fill both soap dispensers on your dishwasher? it seems like such a waste of soap!
It depends on how good your dishwasher is and how good the soap is. If your doing a small, fairly clean load of dishes, try filling them only half way. For larger, stuck on grease dishes, I would fill them up. It cant hurt to do a trail and error though 
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I only do so if my dishes are really dirty or if I’m washing a really big load of dishes. I ran out of liquid soap once and only used one of those dish washer tablets and my dishes came out just fine.
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both?? thought there was only one section for the powder or tablet to go in and next to it a slot for the rinse aid to go in. if u have two only fill one of them it enuff for the wash