DerbyDad:

You don't really need the antifoamer chemical. The primary purpose of adding antifoamer is to prevent foam from being sucked into the vaccuum motor because very wet foam or water could potentially damage that motor.

Instead, just empty your recovery tank more often so that neither the foam nor water gets high enough to be sucked into the vaccuum motor.

Also, the best way to add defoamer to your recovery tank is to squirt it right into the suction tool of the machine when the vaccuum motor is running. That way you have defoamer all through the path way that the soap solution takes so that no foam forms anywhere in the machine.

The recovery tank water was lighter after the third pass because you removed all the dirt that machine could remove with the first two passes. A stronger machine (with a more powerful vaccuum) would have removed more dirty water on both passes and the recovery tank water would have been lighter on the third pass, but that stronger machine would have removed more dirt from the carpet altogether.