In article , Peggie Hall
wrote:

One more time: it's YOUR boat. Pipe it any way you want to and live the
with consequences. If you're lucky--and also more competent and
knowledgable than the "average bear," you won't have any negative
consequences...but I've learned from experience that it's hard to go
wrong tailoring advice to the lowest common denominator.

The real question is: how far removed from the lowest common denomator
are you? These days, a lot of boat owners aren't as far as they'd like
to think they are. Otoh, those who are smart enough to find their way
here are usually are smarter than "the average bear.' At least the
questions I see about sanitation systems seem to indicated that they are.

When it comes to engineering stuff, I'm a long way from the LCD. My
work group builds marine gear that's pressure rated to in excess of
2000m pressure, for example. Specifics of marine sanitation systems,
pretty ignorant. Personally, I think the engineering of marine heads is
ridiculously primitive. The Lavac is about the only one I've read about
that makes sense.

My point is, there's nothing that's real rocket science about low
pressure plumbing runs. You need acess to the seacock no matter what,
and anything below WL needs to be reasonably secure against leaks.
Engineered flex hose with 2 connection points (sea cock & toilet) has a
lot less points of failure - provided it doesn't get abraded - than
anything with many joints, regardless of material. However it does have
its downsides. I just can't accept that worrying about vibration
cracking PVC pipes is a realistic issue in practice provided the pipe
is properly supported. It's just as likely that a flex hose will abrade
through and you don't seem to think that's a concern.

PDW