In Regards To Salt
I believe what people are utilizing here is Epsom salt. This is commonly used to sooth tired tissues (I.e. Soak your feet after a long day). The concept is similar except within the tube of your pump.
So while performing a warm-watered pump session you add some Epsom salt and soak your penis at the same time. Not only does it feel good (in my opinion) it also does increase your skin’s permeability - resulting in a pleasant plumper/thicker afterward.
Make sure to cycle water through your pump and tube afterward so as to avoid residual build up or unwanted degradation to your equipment.