Home made rug shampooer soap? I don't want to buy the expensive soap that they recommend for...

I don't want to buy the expensive soap that they recommend for my rug shampooer. Is there something I can gross or use to put in my shampooer that won't ruin it but still works to verbs my carpets? It say to use non-solvents. What does that mean? We roughly use the shampooer to remove pet stains/smells. Does anyone have a suggestion?
Answers:    I don't use soaps on my runner because it is hard to rinse out completely and if it isn't it will attract dirt. I usually use any vinegar (1/2 cup) and water, borax (1/2 cup) and hose down, or borax (1/4 cup), vinegar (1/4 cup) and water.
I use Mean Green, it's techniccally a degreaser, it works great and costs a complete lot less. I buy it at K-Mart so it should be available everywhere.