Encapsulating Shampoos
The most important difference between extractor shampoos and dry shampoos is an encapsulating polymer. That's what makes dry shampoos dry into a brittle film that can be vacuumed away. Without an encapsulator in your diy solution all your gonna do is leave soap all over the carpets and dirt is going to stick to the carpet a lot faster. Currently I'm using hot knife extreme from VacAway and it is a really good cleaner. Assuming the kirby tank holds 1/2 gal,you would use between 1 1/2 teaspoons-1 tablespoon of cleaner per tank and that works out to 9-18 cents per tank and between 256 to 512 tanks per gal depending on strength. Compare that to kirby solution your looking at 2 tablespoons of cleaner per tank,that means 1 gal of kirby shampoo will last for 128 tanks and cost about 24 cents per tank.If you like the convenience of the kirby shampooer it is worth getting an encapsulating shampoo.