make google your friend, or do a search here. theres bound to be a stack of info re miss silvia. yeah, the manual says not to backflush - but most people (the informed ones) do chemical backflush. some do it daily, weekly, bi monthly, etc. depends on usage .
while i wont give u a money back guarantee, backflushing miss silvia is safe (providing you follow some solid backflushing advice, eg not leaving the pump running for a long time with a blind filter). its probably more simple than you imagine.