# Good acid for cleaning marine toilets

## Problem:

On my boat I have a marine toilet. It is operated with salt water.

The problem is, on the interior of the outflow tubing it accumulates some sort of hard grime. I am looking for a good way to dissolve this grime as it is impossible to replace the tubing.

From experience it is known that citric acid work - but not very well. Also it leaves a "sandy" residue that is difficult to flush.

Does anybody have an idea of what this "grime" consists of - and thus how best to dissolve it?

## Materials:

On hand I have:

• citric acid
• 56% phosphoric acid
• 23% HCl

Materials:

• tubing: PVC
• toilet itself: porcelain
• pump: ABS or polypropylene with selected parts in acetal resin, with 316 passivated stainless steel fastenings, brass weights and neoprene seals and gaskets
• valve: grey, harder plastic

I know this quite vague but am hoping somebody can help anyway.

To my knowledge, marine water contains great amount of $\ce{Ca}$ and $\ce{Mg}$ ions, that gives insoluble carbonates and phosphates. So, most probably, you have mix of carbonates, phosphates and, possibly but unlikely, sulfates of this metals and possibly some organic salts, like oxalates. Carbonates are readily dissolved by $\ce{HCl}$ wich in weak solutions will not dissolve copper, but will slowly dissolve steel. It is more interesting to use $\ce{Na2H2edta}$ . It dissolves $\ce{CaCO_3}$ easily and, to my knowledge, in hight concentration dissolves $\ce{Ca_3(PO_4)_2}$ as well, but not sure in the latter.