Pretty sure he was only doing bungalows that day. Did I hear you say salt wash back towards the end? Haven't heard about that before, what is it?
It's to recharge the water softener filter - the sodium in the salt replaces the calcium build up in the softener. It prolongs the life of the RO...
Great, thank you. Is this part of the RO unit or something I have to buy separately?
Okay - I think looking at Lee's van that he (and I) have Ionic Pro6 systems. They have 6 filters in all.
When the tank on the van is filled overnight it goes through:-
1. A carbon filter to remove the chlorine in the water. That's there to kill all the nasties in the drinking water. However, chlorine burns through the RO membrane so it needs removing first.
2. A 5 micron sediment filter
3. A water softener filter (see above)
4. The RO unit
5. RO Bak - a second unit that saves 80% more water
The water then enters the tank at c. 98% pure. In my case it gets down to 2-3ppm from c.270ppm (at the tap) which is outstanding I think.
6. When it's cleaning time the almost-pure water is pumped through the DI filter to polish it to 0ppm. This DI filter lasts me about 6-8 months!
To answer your question, I don't know where you'd get a water softener filter and of course the salt chamber (except for Ionics naturally) but I'm sure other guys on the forum could help...
Hope that all makes sense?! 
Got a Thermopure and Pro 5 from Ionic
I never worked out how to use the RO Back?
