Like a lot of guys on here When i finish a job i use the water left in the solution tank to rinse the waste tank out with a bit of cut off hose, well even after doing this i looked in the waste tank recently and it was pretty grim

It had white fatty deposits inside that i could not remove, i did not want to clean it out with anything that may cause a foaming problem on the next job, so i got a load of Alltec ultimate master that i have left over and have no intention of using i mixed some up with boiling water and filled the waste tank, left it for several hours thinking this would break this stuff down.
Well after a few hours i emptied the tank and it was still inside in all the awkward places you cant reach, i then had a think about what would break this down and ended up spraying WD40 inside the tank, well this dissolved it on contact, i was a little concerned about the affects it may have on the mastic seals inside so i flushed it out immediatley.
Has anyone used WD40 for stain removal because it is incredible at breaking oil and fat up and may be useful for this, i think you would have to be careful on carpets with any kind of adhesive in them though, making sure you flush it out quickly