"markvictor" wrote

And if you skip the vented loop with your system below the water
line, You stand a good chance of sinking your boat as well, Roger.

Yeah, that's what I would say to anyone else myself while wearing my
boat designer's hat. In this case though, some part of the piping is
going to be above the waterline anyway. A slow siphon into the tank,
back through the joker valve, and out the bowl is possible but would
be pretty slow. This isn't part of the system for operation by head
users. It's just an emergency provision for if we get far enough
downeast that we aren't near a pump out. In that case, we'll nip
offshore and do the deed. I'll be doing all the pumping. The seacock
gets opened just before the pump goes on and closed just after pumping
is finished. The pump will have pulled air into the line so a siphon
can't start even if the seacock should be opened by mistake. I'll
take the handle off of this seacock after closing as double insurance.

Sure, I could sink my boat but I would have to turn off the pump
before the tank was empty and then just walk away so that the lines
would be full enough for the reverse siphon to start. I might be that
absent minded but, when I fly my plane, I look at switches that I
could do thousands of dollars of damage and maybe even kill myself by
flipping at the wrong time so I think I can handle it.

In this case, a siphon break would not add significantly to safety and
would be another potential odor leak and maintenance point.

--

Roger Long