I got one of these awhile back (on sale and with coupons ofcourse)
I also bought the PLAIN Dawn. I noticed on the back of the DIRECT FOAM (I do love this product!) that it says "REFILL WITH DAWN DIRECT FOAM ONLY" well, it cost more than the just plain Dawn (especially if on sale!) BUT I found this tidbit of info:
I take an empty bottle of Dawn Direct Foam and make my own refill solution.
You need VERY LITTLE Dawn liquid detergent to fill your empty bottle! Try 1 tablespoon of Dawn detergent per bottle and then fill the rest up with water. Shake it up to get the solution mixed well and then let it sit for a little while. It seems to work perfectly for me and produces a LOT of foam.
If you use even a little bit too much Dawn Detergent, the foaming will be diminished.
Experiment a little bit and see how it works for you.