I keep the two Host rentals busy all the time now.

You have to take your time and do it right, but I have had people tell me they removed coffee stains from light colored carpet, and restored carpet they thought was trashed. You can also hire a professional cleaner who uses the Host system. Whole school and health care groups have switched to the Host system. If you do it yourself, the key is doing it properly, especially the very first time if you have very dirty stained carpet.

Host CAN clean urine stains, if directions are followed.  I have people all the time tell me how amazed they are at what it removes.

It is impossible to wet clean without getting the entire fiber wet. Every time a carpet is wet cleaned the water soluble glue that binds the primary and secondary backings is compromised.  Whole entire health-care conglomerates have switched to Host because it is natural, biodegradable, removes allergens, leaves no wet carpet, is safe to use because next to hard surfaces. I recently cleaned 1500 sq feet of actual carpet, not just the sq footage of the home and removed stains from varnish from furniture. It involved 'pancaking' the Host and working it in to the pile and leaving it over night, but it came up. I was astonished. Of course it had to be water soluble varnish.

The Host pre-clean followed by the 'pancake' technique can indeed remove urine salts. Using more moisture than was originally in the stain only dilutes it. It might take a repeat application or two, but the principle of absorption is immutable. The sponges will draw the pre-cleaner and the stains and as the moisture evaporates into the air trap it to be removed by vacuuming. Low volume extraction systems still use .8 gal per minute. 85% moisture removal is considered extremely high, and that leaves .32 gal in the carpet for every minute the solution is applied. It's a LOT of moisture anyway you look at it.