I noticed my fuel filter is completely empty after my car sits for a day or two. Don't see any leaks, and I changed the gas cap in case it wasn't venting. Will fill with fuel and car starts and runs after I crank it a little. Is it normal for fuel to drain back through the pump and into the tank?

Its a 1971 318, mechanical fuel pump, one filter in stock location, Edelbrock 600 cfm carb.