CLR? Please clarify what this is.What material is the holding tank? I am assuming plastic, so here goes... Just use CLR to clean it out. This should clean any gunk but more importantly the use of CLR removes mineral deposits and that kind of junk. Then sanitize with lemon scent bleach, both environmentally friendly products and won't harm the plastic holding tank.
Oh yea, I have some in my garage. This is the first time I have heard this mentioned in this forum.A weak acidic cleaning solution.