71 Dart, Fueltank to crankcase vent as return line?

It looks to be the same Dia. as the feed line. Infact both the feed and what im calling crankcase vent run ontop of each other inside the passanger side frame rail.

If it stops rainning today Im gonna blow air in the line and lissen in the tank.
I was thinking of using.the Wix 33040 filter with return nipple after my pressure reg and before the carb.

Is this just a totally bad/wrong idea?

Thanks again.