There are chems that are pre-sprays and designed to be applied and then rinsed off with either an acid rinse or more commonly just plain water.
There are also detergents that are designed to be used in the water tank of a porty or the chem bottle of a TM and used in the HWE process. You can if you wish or if the cleaned item requires it, additional rinse again with an acidic rinse, althouygh this is not neccesary in most cases. Chems disigned to be put through the carpet or upholstery in this manner, do not, as some think, do anything adverse or lead to resoiling. They are designed to be used this way.
Do not confuse the two different types of chems. use as the manufacturers guidelines suggest.
There seems to be some guys out there who just wish to extract with plain water, no matter what. If you do get the correct chems to go with that method.
Dave.