i wouldn't use a check valve or vented loop because they could become fouled with debris and no longer work
I agree with your take on the check valve, but strongly disagree on the vented loop.
Unless the bilge pump discharge is WELL above the waterline (and above the max heeled waterline) there's always the possibility of a siphon forming and filling your bilge with seawater. Although an anti-siphon valve can become fouled either with debris or more often simple salt crystals, they are realtively easy to clean and keep functional.
Bottom line is that if you've got a drain line originating below the waterline that discharges overboard anywhere below the max heeled waterline, you are going to need some type of anti-siphon device to keep backflow from sinking your boat.