Holding Tank Vent line - found water blocking it??

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jefndeb

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Joined
Jun 11, 2018
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601
Location
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Vessel Name
Indigo Star
Vessel Make
2006 Mainship 400
Hello,

Been wrestling with this holding tank vent line issue, and in reading the book from the HeadMistress "Get rid of Boat Oder's", she suggested to rinse the vent line fairly frequently..to help it to not become clogged.in doing so I thing I introduced yet another issue.

During my continued investigation today, I was tracing the vent line and I removed it from the tank fitting just to see if that barbed fitting on the tank was clogged and I noticed that the vent line still had water in it from that last time I rinsed it??

I am guessing this will obviously block any venting??

I suppose it is supposed to be installed to prevent any water from standing in a droop...

Geez......that doesn't seem very possible ...guess I will just replace and re-run a new one...
 
Yes, it should run from the tank up to the side of the hull without any low spots. Low spots will trap water and not let the tank vent properly. Can you find a route that will rise continuously?
 
I will definitely give it a try.....
 
I was tracing the vent line and I removed it from the tank fitting just to see if that barbed fitting on the tank was clogged and I noticed that the vent line still had water in it from that last time I rinsed it?? I am guessing this will obviously block any venting??

Yep...it will.


I suppose it is supposed to be installed to prevent any water from standing in a droop...

That's correct...and the shorter and straighter the vent line is, the better.

While you're installing a shorter straighter vent line, this would be an excellent time to replace the "vent" thru-hull--which are designed to keep sea water out of the fuel and water tanks, but builders use 'em on holding tanks too--with an open "bulkhead" thru-hull as described in my book (thanks for buying it!) with a photo of it. This not only will allow you to put a hose nozzle against it to backflush the vent line, preventing future vent blockages, but will also allow a lot more air exchange in and out of the tank, a key to preventing odor.


It's really important that the vent line be as short and straight as possible. If that requires re-routing it, installing a new thru-hull in a different location is not a difficult job and definitely worth the effort.


--Peggie
 
You should hit the vent line with a short burst of compressed air following a rinse. I would think that the "canned air" products available to blow off a computer keyboard would do the job.

pete
 
Forget about the factory installed vent on the starboard side of the boat. Run a new, larger vent line from the holding tank then under the fwd berth and install a new through hull below the chain locker a little ways above the water line.


There are a few threads on how to do this on the MS 400, I can help you find them if needed. I did this about a year ago, it solved all my odor issues. The vent Mainship installed is too small, poorly located and completely inadequate.
 
Dougcole said:
Forget about the factory installed vent on the starboard side of the boat. Run a new, larger vent line from the holding tank then under the fwd berth and install a new through hull below the chain locker a little ways above the water line.


There are a few threads on how to do this on the MS 400, I can help you find them if needed. I did this about a year ago, it solved all my odor issues. The vent Mainship installed is too small, poorly located and completely inadequate.
Click to expand...
Agrer
I did this last yr on our MS 34HT and it helped a lot. Not very difficult other than drilling the hole for the thru hull. EZ if hauled but could be done it the water if necessary.
 
Wow, what timing on this post! I was just at the tug today installing a filter on my vent line. I assumed the head odors were due to no filter. After cutting the line and installing the bottom filter fitting, I tried to blow into the line to assure all is well. Totally blocked, not a puff got through. I then removed the vent line from the barbed elbow at the tank, and disgusting grey gook came out. The barbed elbow was completely plugged. With the line off it was quite easy to clean that up with a piece of wire. I put everything back together, installed the filter, and now all is well.

With that filter installed, cleaning the lower vent line and elbow will be easy peasy. Just unscrew the bottom filter fitting and run a wire through the elbow.

Based on the responses to this thread, this seems to be a common occurrence. It would be easy to install a fitting on the line near the tank that would be easy to disconnect and allow easy access to clear out the elbow.
 
Toki said:
Wow, what timing on this post! I was just at the tug today installing a filter on my vent line. I assumed the head odors were due to no filter. After cutting the line and installing the bottom filter fitting, I tried to blow into the line to assure all is well. Totally blocked, not a puff got through. I then removed the vent line from the barbed elbow at the tank, and disgusting grey gook came out. The barbed elbow was completely plugged. With the line off it was quite easy to clean that up with a piece of wire. I put everything back together, installed the filter, and now all is well.

With that filter installed, cleaning the lower vent line and elbow will be easy peasy. Just unscrew the bottom filter fitting and run a wire through the elbow.

Based on the responses to this thread, this seems to be a common occurrence. It would be easy to install a fitting on the line near the tank that would be easy to disconnect and allow easy access to clear out the elbow.
Click to expand...


Putting a filter in the bent line will make your problem worse in the long run. It will impede air flow in and out of the tank. If you have odors coming out of the vent line then you are not getting enough air into the tank. The odors are caused by anaerobic bacteria. Aerobic bacteria doesn’t smell. You need more air into the tank and you will not have that odor out of the vent. If the smell is inside the boat then the vent isn’t the problem. If you overfill the tank any the filter will get plugged up by the sewage. Ask Peggie Hall, she is the guru on heads and all things related.
 
Comodave said:
Putting a filter in the bent line will make your problem worse in the long run. It will impede air flow in and out of the tank.
Click to expand...

The filter is in line with a nice, straight section on line. However, it does impede airflow more than if no filter was there. Your point is well taken though, I'll keep an eye on this.

Comodave said:
If the smell is inside the boat then the vent isn’t the problem.
Click to expand...

It seems logical to me that if the vent is completely clogged, then flushing the head will build pressure in the tank, and the only place that pressure has to go is back through the head. Is this not true?
 
Vent filters exacerbate the odor and tank ventilation issues. Better to devote effort to enlarge the vent lines and/or add a second large vent line. There are a variety of methods to add ports to a holding tank, no matter the tank material.

I have a pair of 1" mushroom thru-hull for holding tank vents. When pumping the tank out, I stuff a water hose down the vent with full water pressure to agitate the waste. There may or may not be water remaining in the vent hoses after completion but the first time the VacuFlush pedal is depressed, any remaining water in the hose will be blasted out by the force of the released vacuum and the vacuum pump.
 
Last edited:
Agree with Dave & syjos 1000%
Lots of posts on the subject and Peggie has commented on this often.
At best filters mask the problem at worst they create other issues.
Best to just fix the vent properly and get enough air flow to ensure aerobic breakdown.
 
It seems logical to me that if the vent is completely clogged, then flushing the head will build pressure in the tank, and the only place that pressure has to go is back through the head. Is this not true?

No...and partially. The joker valve is a one-way valve that allows bowl contents and air to pass through it FROM the bowl, not to the bowl. It can allow slow seepage which is why a tank with a blocked vent may not always remain pressurized if the toilet isn't used for several days. But you're likely to find out the hard way just how much pressure didn't escape through the toilet when you open the deck pumpout cap when the tank vent is blocked.


Don said,When pumping the tank out, I stuff a water hose down the vent with full water pressure to agitate the waste. There may or may not be water remaining in the vent hoses after completion but the first time the VacuFlush pedal is depressed, any remaining water in the hose will be blasted out by the force of the released vacuum and the vacuum pump.

I'd think a hose full of water would block the tank vent, preventing the air needed to replace tank contents as they're pumped out from being pulled in. That can result in an imploded tank if the pumpout is a particularly strong one.

The VF suction only pulls the flush as far as the vacuum pump...which pushes it the rest of the way to tank while it restores the vacuum....and that pump isn't nearly strong enough to create enough pressure in the holding tank blow water out of the tank vent.

--Peggie
 
Either way you took a step backwards when you added a filter. Add a second vent, 1” or larger if possible and your smell problem will most likely go away. I was going to add a 2nd vent this winter but could not physically get it done. So I added a Groco Sweetank system to the holding tank. Have done it before on a previous boat and it worked wonders. Absolutely no smell after the install and horrible smell before. What you want is to get more oxygen into the holding tank and the smell will go away. The filter blocks airflow so it will make the problem worse. After the Sweetank in the previous boat we had that boat for 8 years and never added a drop of chemicals into the holding tank and never ANY smell.
 
HeadMistress said:
I'd think a hose full of water would block the tank vent, preventing the air needed to replace tank contents as they're pumped out from being pulled in. That can result in an imploded tank if the pumpout is a particularly strong one.

The VF suction only pulls the flush as far as the vacuum pump...which pushes it the rest of the way to tank while it restores the vacuum....and that pump isn't nearly strong enough to create enough pressure in the holding tank blow water out of the tank vent.

--Peggie
Click to expand...

The VC pump fills the holding tank as it runs and if there is water, not waste, in the vent line, the pressure in the tank builds to a point where it will push the water out of the vent line.

When the tank is being pumped out, any water , not waste in the vent line will get drawn into the tank by the pump suction.

There is very little resistance from water in a low spot on a 1" vent line. It will not allow air to freely enter and exit the tank but any pressure from pumping or vacuum will cause the water to flow out.

If there is waste or TP in the vent line, it may create a block causing tank distortion.
 
When the tank is being pumped out, any water , not waste in the vent line will get drawn into the tank by the pump suction.

Ok..I get it, but it's not something I'd recommend.

The VC pump fills the holding tank as it runs and if there is water, not waste, in the vent line, the pressure in the tank builds to a point where it will push the water out of the vent line.

If the tank is full, or even close to full, it doesn't take much pressure to push waste into the vent. What do you have against making sure the vent stays clear by just sticking the hose nozzle against the vent thru-hull and backflushing the vent line every time you wash the boat and/or pump out? The vent thru-hull is obviously easily accessed from the dock or you wouldn't be able to stick a hose all the way into the vent line when pumping out.

You have to be an engineer...


--Peggie
 
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HeadMistress said:
If the tank is full, or even close to full, it doesn't take much pressure to push waste into the vent. What do you have against making sure the vent stays clear by just sticking the hose nozzle against the vent thru-hull and backflushing the vent line every time you wash the boat and/or pump out? The vent thru-hull is obviously easily accessed from the dock or you wouldn't be able to stick a hose all the way into the vent line when pumping out.

You have to be an engineer...


--Peggie
Click to expand...

I always flush the vent line during pumping out. Post 13

I'm referring to the small amount of water remaining in the vent line after flushing the vent line. It's not always possible or practical to install the vent hose vertical throughout it's length. I have a short section of vent hose that is horizontal due to the boats configuration and a small amount of water is retained after fresh water flushing.
 
Head vent

Sorry, new to posting! I have a 2004 mainship 400 twin 240 Yanmar.would appreciate how you rerouted vent hose. Thanks A.B. Carnathan.
 
I'm not all that familiar with the 400
On my MS 34HT it was easy.
Hatch in fwd cabin exposes fwd end of holding tank and location where factory vent enters tank and then runs mostly hidden to the stbd side of hull.
I simply disconnected inserted the largest size straight barb ftg and ran the hose fwd on top of stringers under the bed platform/ storage space to the bow area. This took some doing with snake, semi rigid PVC tubing, etc to finally reach the bow under the anchor locker.
This area under anchor locker & windless is accessible by removing the fwd bed headboard.
I selected a location near the anchor locker drain and fwd A/C discharge just aft on the port side of the bow. Taped a magnet in place inside and found the location outside. Drilled a pilot hole and rechecked location inside. Then drilled proper size hole for a straight through hull / hose barb ftg using a hole saw. Bedded the ftg and installed. Attached hose & clamps. Removed slack to eliminate sags and attached hose to tank fitting.
Done... time for a beer break!
Hope that helps with other models but you will have to figure routing and access for your situation.
 
Bacchus said:
I'm not all that familiar with the 400
On my MS 34HT it was easy.
Hatch in fwd cabin exposes fwd end of holding tank and location where factory vent enters tank and then runs mostly hidden to the stbd side of hull.
I simply disconnected inserted the largest size straight barb ftg and ran the hose fwd on top of stringers under the bed platform/ storage space to the bow area. This took some doing with snake, semi rigid PVC tubing, etc to finally reach the bow under the anchor locker.
This area under anchor locker & windless is accessible by removing the fwd bed headboard.
I selected a location near the anchor locker drain and fwd A/C discharge just aft on the port side of the bow. Taped a magnet in place inside and found the location outside. Drilled a pilot hole and rechecked location inside. Then drilled proper size hole for a straight through hull / hose barb ftg using a hole saw. Bedded the ftg and installed. Attached hose & clamps. Removed slack to eliminate sags and attached hose to tank fitting.
Done... time for a beer break!
Hope that helps with other models but you will have to figure routing and access for your situation.
Click to expand...

Pretty much the same process on the 400, except easier. Plenty of room to run the hose under the bed next to the fwd AC, no need for a snake.

I cut the hole through the hull even with and just aft of the anchor locker drain on the port side. The drain makes a good reference point.
 
Still Getting Holding Tank Odor...

I have 3 times had a new boat where there was a mysterious - faint - and not stoppable odor.

This seems to have been a result of the vent being only on one side of the boat. In a stiff breeze there appeared to be enough pressure differential to draw air back into the tank or push air into the tank.

FOUND: Odor was escaping through the caps covering the sending unit wires on the top of the holding tank. Fix has been to fill these tiny caps with silicone adhesive where the wire passes out of the sending unit on top of the holding tank. It also worked filling these tiny plastic caps with silicone grease for a customer who did not want to use an adhesive. But I'd stick with using silicone adhesive to assure a more multi-year solution. Silicone adhesive is easily removed and why wonder if simple grease might be pressured out some year into the future.
 
For those that can't get an adequate vent line to eliminate odors here is a link for a DIY tank aerator that I installed on Bacchus. I have since replaced the original metal tube with a piece of PVC but otherwise this works very well. This was before I found the path to the bow and moved & enlarged the vent. May experiment this season to see if aeration is still req'd / helpful or if new vent alone has fixed it completely.

See Tank Aeration Project https://dkloeber.wixsite.com/bacchus/projects-pg-2
 
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