Just got my (new to me) 2007 382 wet this past wknd. Now its on the lift. The manual says to hook the hose up to the flushing attachment and start the engine BEFORE turning on the water. That seemed odd to me. Can someone confirm this? Also there is no mention of putting any flushing attachments to the lower units which also seemed odd since there are forward and side pickup openings. Are they required?

Assuming you have the factory setup like my 353, you don't need any additional flushing attachments. When you turn on the hose, the water will simply run back through and out the outdrives. When you start the engine, the water pump will suck the water in since the flush kit is upstream of the pump. I don't know why you would start the engine first unless you have a closed seacock or check valve upstream of the flush attachment.

Thanks, I was able to talk to a service tech that told me the same thing. These manuals can sure be misleading.

Formula does not want you running water up into the exhaust without the engine running. If any of the water goes past the impeller it eventually cycles to the exhaust. As long as the pressure is low enough it will probably all exit the drives. If some goes past the impeller and up to the exhaust you could get reversion without the engines running. Of course running the engines before you turn it on will fry your impeller. Best bet is to turn the water on and start the engine as simultaneous as possible.

Two minor problems with your hypothesis. One is gravity and the other is path of least resistance.

That is why I said as long as the pressure is low enough it will exit the drives. At a certain point if there is enough water coming into the system, resistance will build up in the outdrive path and the path of least resistance would shift from the outdrives to the fresh water cooling system.

But that could never happen with a 5/8 garden hose and city water pressure.

Probably true - but the thread was about why the manual says what it says. It is called CYA for the factory.

I cant get the male part of the hose to hook into my flush ports. Special adapter needed?

Yes, it screws on to the hose then plugs in like an air coupler. Any Mercury dealer should be able to get it. You might find it online at Bam Marine. He is also a member here so you could shoot him a PM.

My manual said that also, but I always hook the hose up first. Never had a problem.