i add 2 or 3 oz per gallon. might have used it on a split-home apartment, idk. doesn't matter tho, dirty carpet is the same in any structure

I tried some of the 40% stuff STRAIGHT on some pretty bad air filtration lines in a house. Then scrubbed the trial area with a white face cloth. The face cloth did get kind of gray, but both I and my customer agreed that the trial line didn't look much different.

http://www.jondon.com/catalog/product_info.php?products_id=7344

...for soil filtration lines...