I think… if you remove the reeds on the purge valve and install a nipple you will end up wit alternating vacum and pressure pulses cancelling themselves out in you fuel tank the reeds make certain waist oil/gas only goes OUT the crankcase just like the air from your tank pressure nipple feeding air ONLY to the tank.
hope I read your right
in any event if you are worried about crankcase oil reaching the water you could use xd-100 if your consumption is not great $$$ .. xd-100 is more nature friendly
search around I recently saw an oil recovery set-up to send crankcase oil/gas sludge to a spare non pressurized holding tank
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