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Old 10-21-2020, 09:22 AM   #1
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New holding tank vent line hose

I'm in the process of replacing the holding tank vent line (hose that runs from the existing tank to the existing thru-hull vent). At this time I want to keep things as simple as possibie - I'm replacing the vent line hose only.

I need to stick with 5/8" inside diameter. I want highly flexible 5/8" hose with minimal outside diameter.

What type of hose should I choose? How should I attach the new hose to the end of the existing hose to pull it through? Thoughts and ideas are welcome.
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Old 10-21-2020, 10:33 AM   #2
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If you are going to replace the hise why not go to 1Ē and help get air into the tank? I would use 1Ē Raritan Sani Flex hose. It is really good and does not have a history of smalls getting out of it. You can pretty easily put in a larger fitting on the tank and use a standard mushroom through hull fitting as a vent fitting on the hull. Donít let it have any dips on the way out. With this setup you can back flush the vent when you are pumping out. Doing all the work of replacing the hose, you might as well go the extra bit and have a good vent system.
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Old 10-21-2020, 10:40 AM   #3
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Comodave -- Your suggestion is where I'll eventually go. But -- Right now, for a variety of reasons, replacing the 5/8th line is the option I need to stick with.
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Old 10-21-2020, 10:42 AM   #4
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Ok, if you are eventually going to replace it then hose quality probably doesnít matter as much. Most hoses will last for a while before they stink. I wouldnít go with the clear vinyl though.
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Old 10-21-2020, 10:44 AM   #5
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You can use Shields or Trident #148 flex PVC for the vent line. But I have two questions: 1. What do you expect to accomplish by replacing only the vent line...and 2. How long IS your vent line and what kind of tortuous path does it take to make it necessary to connect the old to the new to pull it through?????



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Old 10-21-2020, 12:26 PM   #6
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Peggie - Here's the situation:

The vent line run is about 10' max.

The boat is a Mainship Mark I. The PO replaced the Sealand with a Jabsco toilet emptying into a 25-gal tank mounted on the boats centerline under the floor between the galley space and the head compartment. The OEM head compartment is a fiberglass liner.

The vent line is clear 5/8 hose used for hot water lines. The tank is not fully venting and the problem is strong odor immediately after flushing solids. Pumpouts only get about 1/2 the tank contents.

The thru-hull is a fuel-tank type vent with a 90 deg elbow. The vent itself seems to be clear. One of the vent screens is gone. I can push a plastic wire tie into the open side about 4-5" before it hits an obstacle.

At the bottom of the space between the hull and the liner both the discharge and the vent hoses pass through a wood wedge/spacer drilled out with holes just large enough for each of the lines to pass through. The spacer is well beyond reach.

I don't see anyway to thread a hose through the spacer opening from the top side -- it's way out of reach. So I'm looking to pull the hose through as I remove the old hose.

I don't think I can install a new vent thru-hull until the boat is hauled - I haul in March. Even then, the access to route the hose will still be an issue. I want to workaround the issue now, pending doing the whole system at some future point.
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Old 10-21-2020, 12:49 PM   #7
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Sounds like you need to find a new route for the vent hose to run. If it is that hard/impossible to run a small hose now you wonít be able to get a bigger one through later. I would just bite the bullet now and run a new bigger hose in a different route. You should be able to drill the hole for a new through hull from the dock. I use a couple of rare earth magnets to find where to drill. I find the location on the inside of the hull and tape one magnet to the hull. Then go outside and the second magnet will find the inside magnet. Then mark the place that the magnet was on the outside. You want to drill with a hole saw from the outside so you donít get splintering on the hull side.
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Old 10-21-2020, 01:06 PM   #8
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Quote:
Originally Posted by lucky day View Post
The vent line is clear 5/8 hose used for hot water lines. The tank is not fully venting and the problem is strong odor immediately after flushing solids. Pumpouts only get about 1/2 the tank contents.

The thru-hull is a fuel-tank type vent with a 90 deg elbow. The vent itself seems to be clear. One of the vent screens is gone. I can push a plastic wire tie into the open side about 4-5" before it hits an obstacle.
Perhaps you could use 1" SaniFlex hose -- it really is flexible -- but use something smaller to pull it most of the way?

And/or, perhaps you could use short segments of smaller hose at each end, SaniFlex for most of the run, to take advantage of it's flexibility?

Those wouldn't take full advantage of the larger diameter hose, but...

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Old 10-21-2020, 01:08 PM   #9
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Yes, 1Ē Sani Flex hose is what I would use. Do it one time and it will probably last forever in a venting application. BTW, Defender has the best price on it that I found last winter.
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Old 10-21-2020, 01:39 PM   #10
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I fought a similar problem before I finally decided to install a tank bubbler to get sufficient air into the tank.
Worked like a charm.
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Old 10-21-2020, 01:56 PM   #11
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Bubblers are awesome!
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Old 10-21-2020, 02:57 PM   #12
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New vent... Drill your hole from inside or use the old vent hole. Push a piece of line with a loop out the hole and grab it with a boat hook outside. Put some sealer on the vent and feed it down the line. Use the boat hook to wiggle it in the hole. You can screw the nut on holding it from inside.
Takes 2 people but doable. We did it that way on our Mk III to add a forward bilge pump. I was able to snake a hose down along side the hull behind the sink cabinet and into the back compartment where the shower sump is.
Some day I'd like the replace the tank hose too and make it bigger. That's a long horizontal run from the center mounted tank to the side of the hull. Easy to get blocked.

Added We used a mushroom vent.
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Old 10-21-2020, 03:07 PM   #13
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I don't think I can install a new vent thru-hull until the boat is hauled - I haul in March. Even then, the access to route the hose will still be an issue. I want to workaround the issue now, pending doing the whole system at some future point.

It's POSSIBLE that replacing the water hose used for the vent line with sanitation hose new vent line will cure your odor problem, but it's unlikely. I suspect that'll require replacing all the hoses. Dave's right--find a new location for the vent line that provides a shorter straighter run for it. It won't make any sense to upgrade to 1", but just relocating the thru-hull and replacing the existing 5/8" "vent" thru-hull with an open bulkhead thru-hull will allow much more air exchange and allow you to put a hose nozzle against it to back flush the vent line to prevent blockages.

And/or, perhaps you could use short segments of smaller hose at each end, SaniFlex for most of the run, to take advantage of it's flexibility?

I would not recommend splices pieces of sanitation hose together in any part of the system including the vent line.



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Old 10-21-2020, 04:50 PM   #14
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If you have a long horizontal run you do need the mushroom style through hull so you can backflush it at every pump out. You donít want the stuff to dry up and harden in the vent line or you will be replacing the hose again.
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Old 10-21-2020, 06:45 PM   #15
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It will likely be late afternoon tomorrow before I can get back online. Your responses are great - thanks to all.
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