On the hose?
 

When running the typical Mercrusier BBC on the hose can you turn on the water and let it flow without running the engine?

From lessions from my wave runner I always start the engine and have someone on the ground start the hose a couple seconds before I turn it over. If I do not have a helper and have to do it myself is there a danger of getting water in the exhaust like reversion by letting the water run first? Or is the system basically sealed with no worry.

I have 502 Mags x Stainless Marine with straight pipes.

Thanks - Ray

RAY REVERSION ONLY HAPPENS WHEN ENGINE IS IDLEING,AND ONLY WHEN PIPES DON'T HAVE ENOUGH DOWN FALL.IF PIPES HAVE TO SHORT OF FALL,WATER CAN WORK BACK UP PIPE AND FALL INTO EXHAUST VALE.(ONLY AT LOW RPM).YOU ARE FINE DONT WORRY. RON :)