When we had to use tablets whilst we waited for parts for the water softener, we used the Finish tabs. In fact, dishdrawers come with a trial product of Finish Quantum tabs and Rinse Aid!
By the way, you can put tabs in the bottom of the machine, as in the cutlery basket, they might not get as much water, or make less room (or its just inconvenient when the basket is full). That way, the detergent is always in contact with the water, being continuously heated and will probably work better.
I've got some more photos to share of the drawer's performance, but haven't gotten around to downloading them onto the Macbook Pro... So watch this space!