Smaller size than common 1/2" UPVC check valve very hard to find, maybe metal alloy type but pricey!
Have a spare 1/2" UPVC check valve with threaded ends to let go. Can show u how to fit a 16/12mm hose into that valve using straight adaptors. PM me if interested.
Didn't occur to me to use a filter sock after the FR.
Then it will surely cut rowa scatter & even limit the browning of tank water
whenever replace/top up new rowa. This has been the biggest turn off for me to use rowa consistently.