Polyethelene pipe, MPDE or HDPE for sanitation lines?

Has anyone every used poly pipe for waste lines? It is made from polyethelene just like the tanks so I am wondering why it isn't more mainstream on boats? It appears many European boaters have adopted it. Your thoughts?

We will be pulling into a yard near Charleston next week for some tasks. One of them is replacing sanitary hoses and addressing a shortcoming in the holding tanks initial design. We are replacing the lines with PVC.

I would think that PVC would be ok too provided there are some flexible hose at stress points right?

When I did all of mine last year I replaced a fair amount with PVC. I don't know about using the others that you mentioned. No experience there.

PVC's major advantage is it will not permeate, basically ever. All other flexible hoses will eventually. From what I've been reading on it seems when it comes to any flexible hose the thicker it is the longer it will remain smell free.

Yes the disadvantage of PVC lies in its rigidity, and that needs to be carefully evaluated to ensure there are no stress points

Yes, you want some flexible hose to allow for movement. I found that some places PVC just would not work. In those areas I used a very good quality marine head hose. Also need to use special fittings to go between the PVC and hose. You can get them at:
PVC / Fittings

Roger that is what intrigues me about the poly pipe. It is flexible but also impervious to smells (at least for many many years) just like the holding tanks. Seems like it would be the best of both worlds?

For me it's that, many years part that. We plan on having Moana for many years. I'd rather not have to deal with the issue again later. With PVC I shouldn't.
From what I understand it's in the nature of what makes a hose flexible that allows it to permeate, so all flexible hose will eventually. Comparing hoses of the same material, the thicker the hose the slower it will permeate.

Some Selenes have a rep as smelly boats. We believe to have found out why and are addressing what we feel is a flaw in the holding tank. And we are hedging our bet by using PVC.

I replumbed with rigid PVC seven years ago. Added water traps to both heads and converted the old Raritan heads to fresh water flush at the same time. Zero odor issues to this day. Used flex hose from farm dairy/milk bulk tank installation for the connections. Make sure the system is designed so that there are no up hill points in the hard line runs to the tank(s)...fairly easy with risers just after the bowl (to keep water in the bowl).

I think the biggest problems with PE pipe is fittings. Most of the MDPE and HDPE I have seen uses welded fittings and flanges that permit adapting to other fittings. The plastic welding machine requires factory training to use. So how is everyone connecting this stuff?

The question of connections for us will be settled after we are at the yard and determine the location for each connection, and what we are joining between.

Where the outflow from the heads enters the holding tank is being moved. We have some flexibility as to where to move the connections to, and I'd like to create as long a straight inclined run with the PVC as possible, but still need to discuss this in more detail with the yard. They have actually done this same modification to other Selenes before with great success.

Ok so here is another obvious choice - flexible PVC pipe - like they use on pools and hot tubs? It is all PVC but also flexible and the standard PVC fittings will glue right up. It looks just like sanitation hose too. PVC won't absorb smells either.

From what I've learned, once a hose is flexible, it will eventually permeate.

Bill, I removed about 20 feet of the flexible spa PVC hose. It stunk so bad that I thought I was going to loose 50 lbs removing it. Believe me it does permeate and this was only 5 yrs old. From my experience I would never use it.

Roger: must have been a big lunch.

Bill: When it comes to flexible hose, besides only using sanitation type hoses obviously, the thicker the hose is the longer it will take to permeate. But eventually it will.

Wow that is surprising so maybe there is something to the flexibility that allows it to permeate. I might look at the pvc route too now - they have flexible couplings you can purchase so that might be a good long term fix. Interesting idea too about the trap - I guess the principle is the same as a house - it blocks the smell. Not sure I have room to do that though.

It gets into technical specifics that are beyond me but I've read in more than one book, had explained to me by a few yards, and been told by friends in the business that it really is that simple in the end. There is something physically with the fact that it can bend that allows the vapor(?) to eventually make it through.

On our boat also the heads are plumbed to the bottom of the holding tank. So as the tank fills up so do the hoses, just like in a glass sight gauge for a tank. This fluid is in the hoses basically at all times. That's where our scent is originating from. We are going to plug up those intakes and reroute new PVC plumbing to new points on the top of the tank ensuring we have no level or hang up spots along the way. Its what this yard has done with a few other Selenes, and no more problems.

Wow, they ran the yuk stuff to the bottom of the tank? I can see why you would have oder problems. I would think the PVC to the top of the tank would fix your problems.

Yeah that seems like a no-brainer.

yea, I have to say so far the Selene has proven to be an amazing boat. That oversight in design is the only real issue I see, but all things considered, easy to rectify. Can't understand why they would have done that. Oh well...

billwilletts said:

Interesting idea too about the trap - I guess the principle is the same as a house - it blocks the smell. Not sure I have room to do that though.

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Both "facilities" on our boat are configured with a vanity up against the side of the hull, and the head next to that. I ran the discharge pipes from the head unit into the bottom of the adjacent vanity and then vertical to the vented loop. For the aft head, solid PVC runs down hill from the exit off the vented loop, along the side of the hull behind cabinetry in the aft stateroom and into the holding tank under the cockpit. Had to create some new holes for the pipe runs and shortened one drawer for clearance. Lots of skinned arms and hands. Most of these boats are similar in layout.

By the way, those formed black rubber couplings (with clamps) available at the big box stores are attractive alternatives to barbs and flex pvc hose in some spots. They're specifically designed for sewage applications, although they might odor permeate...don't know. But even if they did pick up some stink after a period...they're dirt simple to change as opposed to that flex PVC. I used them when I replaced the stinking old pump out hoses with hard PVC (keep in mind that these pump out hoses can be odor culprits in addition to the lines from the head to tank).

billwilletts said:

Ok so here is another obvious choice - flexible PVC pipe - like they use on pools and hot tubs? It is all PVC but also flexible and the standard PVC fittings will glue right up. It looks just like sanitation hose too. PVC won't absorb smells either.

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Hard PVC won't but flex PVC most assuredly will...It's highly gas permeable!

Flex PVC is ok for water, but not for sewage because the insides of hoses and plumbing are anaerobic environments. Water isn't organic matter full of bacteria that stinks when it breaks down anaerobically...sewage is. I've seen flex PVC permeate in less than 90 days. All the cheapest waste hose (sched 148) is flex PVC ...as is SeaLand's "odorsafe" brand, which I've also seen permeate in a very short time.

Trident 101/102 (identical except for color...101 is black, 102 is white) is a double walled rubber hose that has a biocide in the rubber formula. 101 has been on the market for nearly 20 years without a single reported odor permeation failure. 102's track record isn't that long only because it hasn't been on the market but about 10 years...it took 'em a while to figure out how to put a white "skin" on 101.

Which is why they're the only hose I recommend. Shields has one they've put a "lifetime" warranty on...but since the useful life of any hose--fuel, water OR waste--is only about 10 years because all hoses do dry out and become brittle with age, "lifetime" is just hype to justify a ridiculous price IMO. Raritan introduced a "new" hose a few years ago...made in Italy. It appears to be same hose that Vetus also sells under their private label brand name. I've never heard anything good or bad about Vetus hose...Raritan's hasn't been on the market but a few years, not long enough yet to recommend 'cuz I tend to stick with known track records, and 20 years with no reported odor permeation failures is by far the best track record for sanitation hose. And it's reasonably priced.

Hard PVC won't permeate, but it's best to use only in long straight runs, 'cuz short runs require a lot of unions, all of which can leak if subjected to enough stress and flex.