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Old 23-09-2021, 11:13   #1
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Trouble getting a good seal on a holding tank vent

First, my apologies if this is covered in other posts. I searched but didn't come up with an answer. Second, I am planning a better long term solution but hopefully what I learn here will inform the long term.

So, I disconnected the vent hose with the good intentions of making it a 1" vent. I also had planned to change the current configuration to either include a macerator or gravity empty. Due to some other priorities I am now just trying to get my head back to a sound installation. I replaced all the 1-1/2" hoses and y-valve (all circa 2005) and they seem secure but first I have to solve the problem at the vent.

The OEM installation had 5/8" Dometic odor safe (at least appeared to be Dometic) going from a 5/8" thru-hull to a 3/4" elbow on the tank. The hose connection on on the thru-hull is smooth. The original tank connection is shown below. Instead of barbed I guess I would call it ribbed but it is 3/4". I tried to reuse the original hose but I can't imagine how they got it to slip over the tank fitting. I tried soaking the hose in near boiling water but it wouldn't stretch enough. So I thought as an interim step I would get some 3/4" hose with a reducer between. Far from ideal but again I am trying to get back to a working head until I have time in a month to change the tank fitting and the thru-hull.

I used the reducer also shown in the photo. It too is "ribbed". The new 3/4" Dometic hose slips on far more easily than I would have expected, especially onto the reducer. All the connections are double clamped. However with a couple of pumps of the handle (air only and the outside of the thru-hull blocked) I can hear and smell air getting past the hose at the tank fitting. I cranked down on the hose clamp but still air is getting by.

The tank fitting worked from the factory but with a hose down one size. Do I need to find a away to get 5/8" hose onto this? Or with 3/4" hose and a ribbed fitting is it critical that the hose clamp not ride on the rib? I've heard of others putting some sort of sealant on the connection before installing the hose but am concerned about compatibility issues between sealant of choice and either the hose or the tank fitting. And sealant seems like I'm avoiding the correct solution.

Thanks for any suggestions.

Harry
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Old 25-09-2021, 05:09   #2
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Re: Trouble getting a good seal on a holding tank vent

I think you're stuck with a 5/8" vent until you can replace the vent fitting on the tank and the thru-hull with 1" fittings. As a short term solution you should be able to get 5/8" Shields or Trident #148 flex pvc hose onto the 3/4" fitting if you warm it a bit and lubricate with little dishwashing detergent (Dawn is good). Don't use any sealant...double clamp with screws 180 degrees apart.

Or, it would be an easy job to replace the vent thru-hull with a 3/4" open "bulkhead" thru-hull and buy 3/4" hose. The open thru-hull would increase the air flow and provide you with a way to prevent vent blockages: just put a hose nozzle against it to backflush the vent line every time you pump out and/or wash the boat. Anything that's tried to set up housekeeping in the vent line just gets a water slide ride into the tank.


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Old 25-09-2021, 10:24   #3
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Re: Trouble getting a good seal on a holding tank vent

Thanks for the feedback Peggie. I have the new 1" thru-hull, elbow for the tank, and hose. Due to time constraints I'll try the other hose you recommend for a 5/8" stop-gap.

Do you have experience with the "ribbed" fittings I show in the photo vs. barbed?

Thank you,
Harry
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Old 25-09-2021, 17:31   #4
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Re: Trouble getting a good seal on a holding tank vent

I've found over the years that it really doesn't matter whether the fitting is "barbed" (ribbed) or not as long as the hose is well onto it (warming and lubricating help) and is double clamped.


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Old 30-09-2021, 08:53   #5
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Re: Trouble getting a good seal on a holding tank vent

Thanks for the recommendation of Trident hose and the rest of your advice. I happened to have enough 5/8" and it was much more pliable when heated than whatever was originally installed so slipped over the 3/4 fitting. She is all buttoned up and no odors or bubbles after a little pressure test. I have the parts to bump up to 1" vents on both our heads next opportunity.
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Old 30-09-2021, 14:47   #6
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Re: Trouble getting a good seal on a holding tank vent

Good! I'll be glad to help you when you're ready to "upgrade" your vent to 1".


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