We have a Lavac head. Like all heads, scale builds up due to reaction between sea water and urine, if users do not pump LOTS of water through.

The main point of concern is the diaphragm pump. Of course I can dismantle it and clean it but that is no fun, and some corners, particularly the key joker valve, are very difficult to clean.

Thw whole system is plastic/rubber, so I am not worried about acids attacking it if used to dissolve scale.

I tried 35% phospooric acid (diluted to about 5% to 10% with water already there) It moves some scale but not all.

I can easily get 70% sulphuric acid in an adjacent hardware store. How strong a mix makes sense? How long to leave in system?

I like the idea of hydrochloric acid better, since calcium chloride is soluble in water, but cannot find any here.