If you intend to use plastic tanks for drinking water then it's wise to remove them on a regular basis and rinse with 'Milton' fluid or similar solution as used to disinfect baby bottles etc.
They are supposed to be UV stable and don't allow any light through that can promote bacteria growth etc but over time you will still get a slime on the inside that should be removed.
I much prefer tanks with port holes that allow you to get a fist inside for proper contact cleaning.
I do rinse my tank out from time to time but only about twice a year.
I use 25/75 off hydrochloric acid and water, takes any slime off instantly then rinse with water a few times and done. never had a problem with taste. I have been doing this with the caravan tanks for 15 years with no problems either.