are flushable liners safe for septic tank

Some are, some aren't. (We're on septic too.) Any of the 'spunlace' liners are fine for septic tanks but not many of the other ones. Personally I find the spunlace ones to be a bit of a waste of time (they're so fine they bunch a fair bit) despite the fact that they feel the nicest. I used to love the Disana ones but you don't seem to be able to get them here any more. We now use similar ones that are 100% cellulose (nothing else to bind them together) but a bit thicker than the spunlace ones and if we use them at home (generally I can't be bothered, but we use them for daycare and he sometimes comes home with one in the nappy he's wearing) I will throw them through the washing machine - they will withstand 3 or 4 washes before starting to disintegrate, and at that point I have no qualms about flushing them