The amount of 'gunk' in the tank also depends on what you're using as a cleansing liquid. I mostly use organic solutions for my stage 2 cleaning, L'ArtduSon or Tarkett BioClean. And they do leave more residue which allows mold and stuff to form in the tank.
(I always use an Isopropyl/Pure water/Washup liquid in the first part of cleaning a record)
I've had my Okki for about four years and it was sent back once due some strange effects. There was a constant hum when not in use, but connected to mains. This seems to have sent out some galvanic currents in different parts of the machine which caused corrosion. This mainly affected the suction pipe which lost its surface treatment and of course stopped it from moving freely in its mount.
The other issue was that the center tap on the platter had too few and too loose coils exposed which in the end caused med to strip them... :/
Anyways, my machine was repaired, the faulty electronics board was exchanged, the suction pipe was renewed and the the center tap was rebuild by a workshop, replacing the coils for one with more than a centimeter of coils, and much tighter.
However, there is still a very low hum when mains are connected and due to this i never leave it connected when not in use.
Function has always been top notch though, except for the issue with the coils that is!

/Mike