I think it's near impossible to give them a thorough clean inside all I done was purchased some liquid Milton emptied the water tanks, poured the prescribed amount of Milton into each tank then filled them up with water and run some through all the taps and let sit for the required amount of time then I drained all the water out put about 20/30l into each tank I left that in there to slosh around while I drove to the next town, drained that again and filled them up.