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Old 28-05-2007, 15:59   #1
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PVC piping in marine sanitary exhaust

Hi, all,

In the rec.boats.cruising usenet newsgroup, there's a conversation happening
on marine toilets. This thread included this snippet from me; it may be of interest here:

On May 17, 11:38 pm, Don W <donw_s11atswbelldot...@figure.it.out> wrote:
> RW Salnick wrote:
> > I'd skip the use of the head hose, except as for flexible connections to
> > hard-mounted items, unless the runs are very short. Instead, plumb with
> > rigid white PVC pipe - it has an essentially infinite permeation time -
> > unlike the hose.
>
> > bob
> > s/v Eolian
> > Seattle
>
> Hi Bob,
>
> I'd love to plumb with PVC pipe, but I've heard
> that the flexing of the boat causes it to develop
> cracks over time. Is that true?
>
> Don W.

Hi, Don, and group,

I'm not an expert, but I can provide some RW experience.

Most of you know that I had about the most boat flexing one can experience
and still float, after it's over, a few months ago.

Before that time I had installed PVC exhaust plumbing on both heads. The
forward head, which I'd originally thought would be impossible, turned out
to be feasible with lots of joints, and some creative vocabulary. The aft,
which I originally thought would be a piece of cake, I then thought couldn't
be done at all, actually turned out pretty simple.

However, I learned a bit along the way. As nobody's going to be grading you
on neatness, slop the crap (pardon the expression) out of the joints with
cleaner, and then with the glue, when you're making the assembly (do it all
dry first, of course, and allow for the full depth of insertion as the glue
will act as a lubricant, letting you seat it fully where it won't go, dry).

I didn't do that in my forward head installation. As a result, I had two
very minor seeps at two joints after the incident (more below). Those were
cured with careful sanding and addition of, first, more glue preceded by an
acetone wipe (to clean and soften the plastic), and followed by some
penetrating epoxy (more flexible than laminating or general-purpose epoxy)
with a thickener added to keep it in place. As I'm currently on the hard, I
shut the thru-hull connection, opened the anti-siphon valve (like you'd see
in a laundry connection), and poured water into the system until it was full
(both toilet and hull ends of the line), and waited a week. No seeps. The
aft didn't leak anywhere.

So, from that, I get...

First, if you think you're being ridiculous in your application of cleaner
and glue, and follow up each joint with swabs around the perimeter for good
measure, it's unlikely you'll ever have a leak.

Second, if there *is* a very small leak, it can be addressed, if you can get
to it. I'd originally thought I'd have to cut out the offending joint - but
even that's possible to do.

Meanwhile, as an establishment of the bona fides of this process, this hard
pipe stood up to huge hull flexing and pounding (impacts) - more than you'll
ever encounter in normal seagoing life. As seen in my "Thanksgiving" post,
I estimate, based on time and wave interval, that our hull took not less
than 3000 and probably more than 5000 huge crashes on rock. The flexing our
hull provided in her defense is totally awesome, and for which we're without
words to adequately express how grateful we are that was so. From that I can
provide my own assurances that, done right (joints fully glued) and
supported (no flailing around) that it's unlikely you'll ever have to deal
with that again.

Given the stench of the hose we took out (the good stuff), I'm very happy to
not have to face that thought in this boat's lifetime. Meanwhile, I have the
15' of AVS96 that I bought to do the forward head available, now (after the
wreck, I'm sure I won't need it), should anyone want it.

And, finally (you knew I'd get here, eventually, right??), for those so
inclined, my galleries have the gory details on the installations of both
heads' hard pipe, and I can give you the links if you like. However, in
general, I think the forward head (the more complex of the two) was Feb06 in
the refit gallery.

Hope that helps...

L8R

Skip

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Old 29-05-2007, 02:05   #2
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Skip, I too use rigid PVC in my boat. I have no problems at all with it. Some of it is hard fixed all the way to the basins and aft toilet and one is fixed via a flexible hose from the forward toilet. The flexi coupling is so I could fix a vented loop to that toilet being and electric unit.
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Old 01-06-2007, 07:22   #3
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Are you guys using rigid PVC to a seacock. I was told by a surveyor that this was against CGG regs and I would have to redo the connections with double walled hose and two stainless clamps for anything below the waterline. The PO did a beautiful job of this and I hate redoing it. There are only the Galley sink and wash basin set up like this. Any experience with this out there.
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Old 01-06-2007, 14:53   #4
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No my PVC is from basins and Toilets to holdign tank only. From macerator to seacock, it is flexible.
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Old 01-06-2007, 17:45   #5
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Quote:
Originally Posted by Lancerbye
Are you guys using rigid PVC to a seacock. I was told by a surveyor that this was against CGG regs and I would have to redo the connections with double walled hose and two stainless clamps for anything below the waterline. The PO did a beautiful job of this and I hate redoing it. There are only the Galley sink and wash basin set up like this. Any experience with this out there.
Before I discovered how to do it directly (see below), I used a short piece of AVS96 to connect between the PVC and both ends of the chain. There's a piece between the tailpipe on the toilet and the PVC, and also between the end of the PVC and the Y valve (which also has a flex on it to the through hull, and flex piping to the holding tank, which was new when we bought the boat, but's never been used, and we really don't expect it to be used, so it's sort of irrelevant).

However, on the stern cabin, the PVC runs directly to an ell in the line at the through hull, and to the straight-through tailpipe from the toilet.

Both were put so as to be flush (pardon the expression) connections. A standard rubber coupling hose was put over both of those (the same as was used between the end of the forward and the Y valve). The single clamps on both ends were supplemented by a third clamp right over the (reasonably tight/close, very small clearance) joint, preventing odors from escaping should they succeed in saturating the rubber.

And, of course, the coupling is trivial to replace at a future time, and allows easy access for disassembly (as I had to do to the aft cabin's head to redo my drive shaft and shower connection just recently).

I'll have to replace the small joints of the hose in the forward head, from time to time - but they're short enough that the resultant odor shouldn't be a problem for several years, there, either.

Hope that helped...

L8R

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Old 09-08-2007, 07:59   #6
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Hi All, I am in the process of refitting/upgrading most systems aboard my boat. She was a Great Lakes boat, so no overboard discharge. In addition to adding an overboard discharge, I am replumbing the pumpout portion of that system. I am using 11/4 Sched 80 PVC for both O/B discharge & P/O flow. My question is: is it a problem if I use 3/8 Sched 40 PVC for the Vent plumbing? I want to avoid any Odor problem and only do this once. I plan to use short, flexable, connections to Y valve, discharge pump, and thru hulls. Any advise would be welcome. Thanks.
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Old 09-08-2007, 08:21   #7
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Bigger is Better & Flexible is Better than rigid:

Holding tank vents must be designed and constructed to minimize clogging by either the contents of the tank or climatic conditions such as snow or ice.
The U.S. boat building industry seems to have settled on 9/16," inside diameter (ID) or 5/8" ID hose as a suitable vent size.
In Europe the latest draft of the ISO standard requires one of the following:
1.) that the vent line has a 1 1/2" (38 mm) ID: or
2.) that there be multiple vent lines of at least 16mm, which together add up to an equivalent area; or
3.) that there be a vent line of at least 12mm, combined with a vent valve on the tank, which has an opening of 38mm, and a notice close to the pumpout fitting on the deck stating that the valve must be opened before pumping.

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Old 09-08-2007, 14:21   #8
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Quote:
Originally Posted by GordMay
... In the holding tank, the key to odor control is the vent line; it must allow a free exchange of fresh air for the carbon dioxide generated by the sewage ...
I keep reading this, and I know Ms Hall has a cult following and has sold a lot of books, but it makes no sense. Speaking as someone who ran a sewage treatment plant and understands the technology and biology involved there is NO WAY that passively venting a tank of waste will supply enough oxygen into the liquid to keep it aerobic. That requires active mixing and a lot of it.

Think about it for just a minute... If you filled a bucket with holding tank "stuff" and put it on deck, the proponents of this approach would insist it would not smell. Really? Even an open bucket of waste will become anaerobic because the bacteria involved grow so fast then consume all of the dissolved O2 faster than it can diffuse into stagnet liquid. If you stir it, or bubble the air below the surface, it's a different story.

A well constructed holding tank system does not leak oders into the boat. It just doesn't. My tank and system doesn't smell, and it is a flexible tank with no head space at all a fairly small vent.

Large vents might not clog as readily as small ones, and that is good, but the are not by themselves going to fix holding tank smells by allowing the material to become aerobic.

People who have rebuilt their holding tanks with this advice and notice an improvement should credit the rebuild, not the magic large vents.

I keep reading as well that boats in Europe have these large vents, but I have never seen one. Can anyone point to a brand that is built this way today?
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Old 09-08-2007, 14:29   #9
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Quote:
Originally Posted by GordMay
In Europe the latest draft of the ISO standard requires one of the following:
1.) that the vent line has a 1 1/2" (38 mm) ID: or
2.) that there be multiple vent lines of at least 16mm, which together add up to an equivalent area; or
3.) that there be a vent line of at least 12mm, combined with a vent valve on the tank, which has an opening of 38mm, and a notice close to the pumpout fitting on the deck stating that the valve must be opened before pumping.
Gord,

Is that ISO 8099? Is the full draft on line somewhere? The 2001 version does not contain such language, ut rather keys the size of the vent to the size of the tank.

ill
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