That anti-siphon should be located up inside of the gunnel as high as possible. Both on my 400DA and my 52DB they were well up in the gunnels; significantly above the water line.So far, we've had our 98 450DA for a few weeks and have been loving it. It hasn't been all smooth sailing, but over-all it has been a great addition to the family.
We sucked water into the Westerbeke on our first try. Didn't over-crank it or anything - it's not my first diesel or generator. I'm thinking that it was a perfect storm of weight distribution that lowered the transom enough to make the difference between "almost too low" and "too low" - which put the siphon break below the height where it should be in relation to the engine. At the time, we had full fuel tanks, full fresh water and a giant TNT lift on the back. In my forum surfing, it seems that some guys have nothing but trouble with their Westerbeke and some guys have no problems at all and love them. I'm wondering if the difference is in the weight distribution? For example, guys with standard swim platforms and no Cablemaster have a center of gravity which is forward from the CG of those of us who have all of that gear on or aft of the transom. All that additional weight so far aft possibly lowering our transom and lowering the generator in relation to the water line.
I don't know - just a thought - while the mechanic was pumping out my cylinders.
We pickled the engine for a few days until a newer version of the anti-siphon valve arrived from Westerbeke and then pumped out the oil. Drained and flushed the oil, ran for 15 minutes, drained and flushed again, ran, drained and replaced the filter. All seems to be running well now. I'll be extending the hoses leading the the anti-siphon and moving that up as high as I can to eliminate the chance of this happening again.
Something else we noticed - it would be very easy for the tiny rubber one-way anti-siphon valve to be installed backwards within its cap, rendering it useless. Dumb, i know, but easy to do.
Some pics: