3/4" gravity enough to flush/ winterize?

Wouldn't a pump be easier and more sure? I'm thinking if they suck more than the hose can handle it might form a vacuum you won't know about until it's too late.

If you check out this recent thread, starting from post #40 you can see what I did in my boat for the same purpose.
And even if I don't think I mentioned it, the valve I fitted on the strainer lid is exactly 3/4" (with an adequate size hose).

Now, two considerations:
1) I'm not sure of how the water flow demand from your raw water pump compares to mine. But since in my engines it must deal with a 15 liters block with an 800hp output, I'd be surprised if your raw water pump should be more thirsty (so to speak) than mine.
2) When I flush my engines with the system explained in the above thread, I use a hose connected to the dock fresh water supply, so it doesn't go down just by gravity, but it's also pressurized (at least around 30psi, if not more when there aren't other boats using fresh water along the same dock). So, the flow is bound to be somewhat higher compared to gravity alone.
But again, considering also the difference in engine size and power, I would be confident that the flow is OK in your case, also taking the pressure out of the equation.

Anyway, if you arrange a permanent fresh water connection (regardless of whether made like mine or not), you surely must fit a valve and some kind of hose connector, which allows you to use also a pressurized hose for the flushing, as I normally do. And after a good fresh water flush for say 10 minutes or whatever, the last bit of filling the blocks with gravity fed antifreeze will only take a couple of minutes, if that.

"Water Pressure: The New York State Department of Health standard indicates that normal water pressure in the distribution system should be approximately 60 to 80 psi and not less than 35 psi while maintaining a minimum pressure of 20 psi under all conditions of flow."
So you should have no problem with your regular flush outs, but I'm not sure that gravity feed will be enough for the winterizing. That's why I suggested using a pump for that. Cheap insurance.

FWIF I winterize my 6-92's through the zinc anode plug in the heat exchanger. Pump antifreeze in till pink comes out exhaust pipe. Then open caps on sea water pumps catch whatever comes out in pan and done. Very simple 20 years no problems. You also get to check impellers yearly.

3/4" in how long of a hose? From where to where?
Are you going to use the engine pump to move the antifreeze into & thru the engine?

Great idea.
I ad acid/cleaner thru my zinc plugs.

And do what?

With what you provide so far, I'm I'm guessing at what your doing;
You think a lighter liquid is going to push the heavier sea water out of your engine and get charged with the antifreeze from a few foot drop?

I need to start drinking again.

I use an electric pump 1 hose in 5gal bucket antifreeze the other hose connected to 3/4 by 6 brass nipple with garden hose adaptor screwed into zinc plug hole. Hoses are washing machine supply hoses 4ft long. Bucket and pump on floor of engine room. Hope that helps.

+1 on the pump.

Use that RULE slim line submersible electric pump, they're around $100 for the 500 gph version and work very well. I use them for transferring diesel all of the time.

https://unitedstates.xylemappliedwa...h water, seawater, antifreeze and even diesel.

You did not mention with the engine at idle.
With that, your going to need more solution than in that jug.

In the other thread and what jerryd above suggested needs to be read over again.

Other recent thread;
https://www.yachtforums.com/threads/winterizing-40-open.33632/

I am sure YF has more threads on this so please do some searches for more ideas.

I remove the impeller and close it back up. Then there's a hose barb plumbed into the strainer. Pump until pink comes out the rear end. Removing the impeller removes the obstruction in the system so you CAN pump through, and it gets to not sit in the same position and "set" for those months. And, you're combining maintenance and winterizing into a single operation. Haven't decided on a replacement interval there yet... probably every other year.

To the OP.... can't answer the question with (a lot of) data and math, but to my gut a 3/4" feed sounds insufficient. I have seen the "lazy river" coming out of my exhausts at idle and sucking all that through a 3/4" hose sounds like it would not be easy. I decided not to do it this way. The general sentiment on this page seems to lean that way too. Beware of bias confirmation.

"til you see pink" is not a reliable indicator of how well you have protected your equipment. I recommend the use of an antifreeze refractometer to ensure you have flushed the system of fluid that will freeze.
Antifreeze comes in differing grades based on temperature. We spent a little more money on the -100 as opposed to the -50 for added peace of mind.
Be aware for New Englanders, that this year some bad antifreeze got manufactured and distributed:

I have a refractometer. If -50 is not enough we have bigger problems than the toys freezing.

- 50 is probably fine for yall south of the mason dixon. With that being said, let' realize that it is a -50 solution in the jug. How do we account for the mixing that will inevitably take place in those spaces we are trying to protect?