Sewage plumbing

[larryeddington]

I am replacing both my tri cab toilets with sea-land versions of the venerable Mansfield. Aaron has written that the Mansfield does quite well but mine are leaking and no parts for them so using the same thing from se-land. My question is the plumbing, I am changing out all the hoses and rebuilding the two macerator pumps. (y valve is gone already), Is there any reason I cannot use schedule PVC for all but the areas I need flexible pipe? I believe PVC is not permeable.

[WayWeGo]

You are correct that PVC is not permeable, but you need to be very careful to support it so that it does not crack and make sure that the ends and any other flex areas are made up from a good quality sanitation hose.

I used Trident Premium hose for our sanitation system. It is not cheap, but I only needed about 10'.

[larryeddington]

Thanks we will endeavor to make the best connections possible, strap it down and cushion if needed.

At another website "cruising" all seem to think it is best and none have had any problem with it cracking.

In any case going to use PVC.

[BobCT]

PVC is incredibly strong, I can't imagine any scenario where it could crack on a boat. Maybe the joints but it's pretty hard to screw those up if you use primer and cement.

[larryeddington]

that is my opinion, pretty darn strong stuff.

[P-Dogg]

I used clear PVC pipe to the extent possible when I did my heads. If you have long runs, be sure to allow for thermal expansion.

[bjanakos]

The little vibrations you get from running and cruising may cause the material to get brittle. It the same reason why most cars have a piece of flex pipe in the exhaust system. So long as you use a length, say 6" or so on either end of your runs you should be good to go.

[Reel Easy]

Make sure to use primer not cleaner. Or you will not get a full solvent weld.

[Big D]

...Is there any reason I cannot use schedule PVC ....

In fact it is preferable. Having said that, in a Vacuflush system, flexible hose can be used in the suction side between the toilet and the vacuum generator since that line is always empty and only acts as a transfer line during a flush cycle. Once the cycle ends, the hose is empty again due to the vacuum, hense flexible hose is acceptable at this location because nothing sits it in for any length of time. My recommendation though is that you get the premium hose that Dometic manufactures. Keep in mind that the more flexible a hose is, the more permiable it is.

When selecting a location for the vacuum generator, try to position it higher than the holding tank and as close to the tank as you can. I believe the generator can be 50' max away from the toilet. By being close to the tank and higher, anything in the hose will naturally drain down hill and minimize waste sitting in the hose, this is what causes permiation. If you can't mount the generator higher than the tank so things flow/drain down hill, this would be where you want the PVC as you will always have waste sitting in the line between the generator and the holding tank if the generator is lower than the tank. Make sense?

[larryeddington]

thanks but using macerator transfer pumps from the two sea lands. Not using the vacuflush.

[Big D]

Same principle applies. Using a pump to transfer waste will leave waste in the line. As soon as it starts sucking air, waste tranfer will diminish. Lines that will have any amount of waste sitting in them for any length of time should be a ridgid line product unless you use one of the premium sanitation flexible hose products. I think there are a couple on the market that claim to be impermiable. It's due to newer technology in the inner wall of the product. Having said all that, a cheaper product will be smell free for a while, really depends on how long you think you're going to keep the boat or whether you're okay with replacing the lines again when the odours return in a number of years.