well my RO-MAN 60 gal RO came with a gate valve that you turn to flush the membranes
as for chaning the pre-filters, i havent i near 2 years, its still outputting the same amount of water and still works fine --- people say not changing them will ruin the RO membrane, but ive had my money out of it in 2 years so i will then replace the whole unit for 70 odd quid from RO-MAN