Safely removing sodium hypochlorite crystals from hard-to-reach surfaces

I have a small bathing whirlpool which wasn’t used for over ten years. It is built into the ground and I cannot reach the disinfectant container to replace it with a new one. I can access the fill-pipe for the disinfectant which read „Sodium Hypoclorid“ at the time of the last disinfection.


When I open the 1 cm-wide diameter pipe to fill the disinfectant in, I see a layer of half-transparent salt-like material, thus my question:


Assuming that the disinfectant within the container is solid, is there some (safe) method where I can add some special solvent and then rinse the whole container so these crystals go away?




Standard [sodium hypochlorite disinfecting bleach](https://pubmed.ncbi.nlm.nih.gov/28722950/#:%7E:text=Bleach%20contains%203%25%20to%208,which%20are%20not%20covered%20here.) is a mixture of $\ce{NaOCl}$, $\ce{NaCl}$, and $\ce{NaOH}$. The sodium hydroxide, also known as lye and caustic soda, is employed to capture $\ce{CO2}$ that can lower pH via carbonic acid. The latter product reacts with hypochlorite forming the more active and unstable hypochlorous acid $\ce{HOCl}$, that has an even much reduced shelf life than hypochlorite.


Now, why $\ce{NaCl}$, because the [commercial preparation of chlorine bleach](https://www.serviceindustrynews.net/2021/05/14/history-of-chlorine-production-and-use/) is from the action of chlorine on $\ce{NaOH}$, producing equal amounts of both $\ce{NaOCl}$ and $\ce{NaCl}$.


With time, the present of even dust particles with traces amount of transition metals will breakdown the $\ce{NaOCl}$ into $\ce{NaCl}$ and some problematic $\ce{NaClO3}$ (chlorate).


Since this is evidently very aged bleach, the only problematic residual compound is the chlorate. To remove the latter, the less messy dry route is to mildly heat with a small blow torch, as to quote [a source](https://www.angelfire.com/ok2/kelouise/excel/DecompSodiumChlorate.pdf):



> 
> Sodium chlorate, NaClO3, is a colorless, odorless, white solid that melts at 248°C. When heated above 300°C, it begins to lose oxygen. The ultimate products of the thermal decomposition of sodium chlorate are oxygen gas and a white solid.
> 
> 
> 


where the white solid is yet more $\ce{NaCl}$.


Other paths include the use of liquid sulfuric acid, methanol,..., and there is an associated release of toxic/explosive chlorine dioxide $\ce{ClO2}$, which is a path best avoided, in my opinion.


After the heat treatment, just collect the dry salt or water hose it away.


Some references, on the [decomposition of hypochlorite](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/chlorate) and [also comments here](https://cdnsciencepub.com/doi/pdf/10.1139/v56-068).


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