I've a plastic water storage tank as such with a small lid (12"/30cm in diameter).

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It has developed a thin slippery/shiny layer inside of the walls overtime and surface of the water has the same texture.
This tank, as far as I can remember, does not have a drain near the bottom.

My question is,

  1. what is that sticky film/material?
  2. how to get that sticky film/material off the walls and base?
  3. after (2), How to drain all of the water completely and easily, without moving the tank?


1 Answer 1


answering the questions in order:

  1. "slippery/shiny layer" sounds like a biofilm, and there may also be layers of precipitates (e.g. iron or manganese oxides) embedded. Some of the organisms may be innocuous, but some could be pathogenic. There is a US EPA paper on the specific organisms found.

  2. Chlorine-based disinfectants (basically, hypochlorite bleach) and lots of scrubbing should get rid of the film.

  3. A sponge, perhaps on a stick should soak up any standing water after siphoning off most of it. However, sodium hypochlorite is safe to ingest in drinking water if sufficiently diluted, i.e. 5 to 10 milliliters of 1% sodium hypochlorite solution in 20 liters of water, so there is no problem if some is left after cleaning..

  • thanks for the answer. is there are way that I could get rid of the biofilm with only little scrubbing since the lid of the tank isn't large enough for me to get into and tank is large enough to not be accessible from inside easily (stupid design, if you ask me)? Any compound that just gets rid of it if put in water? BTW I havn't been to a hardware store/home depot looking for cleaning brushes for large tanks yet.
    – Ejaz
    Commented Apr 30, 2015 at 14:03
  • It depends on how adherent is the film... bleach alone might remove it; give it an hour or two to work. As for the brush, a sponge on a stick should do. Commented Apr 30, 2015 at 15:08
  • 2
    @Ejaz We use a 14% solution of sodium hypochlorite to clean this kind of gunk out of bilges, or even most marine growth on ship hulls. This concentration is not yet immediately dangerous but gets rid of these films without any scrubbing. Make sure you don't get any into your eyes and if you do, clean with plenty of water.
    – Flint
    Commented Sep 21, 2017 at 19:45
  • As @Ejaz suggests, be careful on skin and clothing (not just bleaching, but, eventually, holes) and do not let 14% sodium hypochlorite sit on glass, as the alkali will etch it after a while. It should be fine in a plastic carboy, but rinse well before use. Commented Sep 22, 2017 at 1:37
  • If cost is not an issue, you could use a new cotton mop that reduces the chances of scratching the surface but provide sufficient friction to work through the film to the surface of the tank. It's use would be restricted to appropriate storage and care after application. The bleach helps to ensure aseptic treatment.
    – Stan
    Commented Jul 20, 2019 at 1:56

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