Working on a neighbors Formula 419 with triple 525sc's. He just bought the boat as a project. Was a Florida auction boat so its corroded and filthy. First goal is to get engines running. Installed 3 new carbs and fuel lines and changed supercharger oil. Shes ready to fire up off an aux fuel tank. Looks to me like the engines draw in water from a bulkhead fitting on the hull and not from the Bravo drives. I cant be sure as its difficult to see under the engines. If its a bulkhead fitting, how do I run one engine at a time on a hose? Or can I?

Im not sure i would run any water thru the motor before checking the exhaust, unless your know its good, but you said it was from Florida. Feed the seawater pumps direct by running a hose to the inlet 1 1/4 .
maybe add a T fitting so you can run on the hose after you get back on the trailer. I assume they have gen 5 sea pumps with mech fuel pumps. might want to pull them, change the gear oil and check the rubber, and maker sure fuel pumps are not leaking into gear oil cavity.

ok , i see the mech fuel pumps , so check that out, only takes a few mins and with new gear oil you wont wipe out the cam lobe in there, not sure what gen Stainless marine exhaust you have, but that can be pressure tested also.

If you didn't know, the front and rear of the blower have separate gear lube reservoirs. Just use the Merc HP drive lube.
The 525SC intake manifolds do not like salt water.
Here is a pic of my inatke and it had less than 200hrs of salt usage and was flushed after each use. HELP!!! Need Merc 525SC Intake

Thanks Griff, I did change both front and rear oils. They were easy with the carbs off. Im also expecting the intake manifolds to be rotted out. If it hydrolocks or gets water in the oil, its getting parted out. I might just buy one, rebuild it, and put it in my Baja 272.

I have one mint 525sc intake left. pm if needed i can dig it out.

Get a piece of hose that fits the seapump inlet and from lowes/hd fashion up a coupler ( used to have one w/ a 1/4 turn valve)

or, ya know, these things

https://www.iboats.com/shop/perko-fl...saAo6CEALw_wcB

Does it have water pick ups for the engines on the bottom of the transom?? Just connect a hose to them.