What's wrong with running it back to the fuel fill? No vacuum to pull it?

My blower set up had it going to the base of the flame arrestor, but if the pump were to rupture, it would for sure had dribbled around the choke tower base (basically useless imo).

Any fitting that would dump into the carb throat.
You can drill thru the side of the choke horn just below the flame arrestor flange and press in a brass tube fitting.
As several have stated, it doesn't "do" anything unless the pump diaphragm ruptures. Its purpose is to dump fuel DOWN into the carb throat.
If you install a fitting on your flame arrestor, it needs to be on the neck, not on the flat plate.

I don't have that issue anymore because I'm running MPIs, but with my Nickerson carbs on the blower (no choke horns) the only place to plumb to was on the arrestor. It was a simple 1/8 nipple that went into the outside portion of the base. This was done prior to me owning it. I had thought about connecting a stainless tube that would extend into one of the carb's airstream, but I ended up selling the boat when I got my 311.

The older Mercruisers (TRS era), actually ran the hose to a glass sight bowl...

I hate to disagree with some, but I have even seen flame arrestors with fuel vent tube in the screen like the below:

I've used those on single carb stuff before.

When it comes down to it, I've never seen a leaking belt driven mechanical pump ever put out enough fuel to fill the tube. All that I've seen, leak just slightly and the fuel leaks into the cam housing. The fuel mixes with the gear lube and over time deteriorates the seal and then it starts leaking out into the water side. If left long enough the water starts leaking out the housing into the bilge

^^^this is exactly what I'm dealing with right now and there was only a couple ounces in the hose. Not sure it would have ever made it to the carb. Maybe if you ran it for a while with a bad pump. Also on the stock hp500 the tube goes to the screen on the back of the aresstor from the factory.

It seems like the problem solves itself. Should the diaphragm rupture enough to dump gas the motor pretty much stops dead. I guess if the pump was lower than the fuel tank with no anti-siphon valve then that can be an issue. How many boats have caught fire due to a bad pump?

I disagree. Before the dinosaurs died and cars had mechanical fuel pumps and carbs, a few times a year i would get in the shop a car that still ran but sprayed fuel out of the weep hole. You do not want this to happen in a boat !

Edit in: the weep hole is where the marine version has the nipple stuck in it to connect the hose to the FA or carb.