The head system in my 1998 400EC needs some explaining. It's the vacuum flush variety and I'm guessing that no upgrades beyond factory have been put into place. I haven't been able to crawl back to the tank and follow lines, but I've been craning my neck trying to see how everything is plumbed. It looks like there's a bottom discharge and I have a pump out plate on the deck. I need to know where the valve is for switching the output. I'll be pumping out at the marina 98% of the time. I'd also like to know how to activate the macerator for discharging into the ocean when appropriate. The owner's manual is slightly less than helpful.