I drive Toyotas all day, you always get at least double what Toyota quotes in manual.
It's so you don't suck your tank dry and pick up all the crap from the bottom of the tank.
Not good for your engine...
I always take my cars back to dealers.
If you have full lexus service history, i'd continue to service with them.
Brighton Lexus (Nepean Hwy, Elsternwick) offer a loan car, car wash.