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Old 08-11-2019, 13:59   #1
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Worth the effort? Extra black tank vent.

Our marina recently installed a new pump out system that really sucks well. Their old one had the screw in head and a pump that seemed to take forever to get all the wrinkle neck trout swimming upstream.

New system had a 'stopper/cork' like connection that's held in place by the great suction created by the system. While the dock hands and neighbors haven't reported any issue, I just have this tingling on the back of my neck that the suction may be strong enough to put a crack in our plastic tank some day.

Our tank vent seems to work just fine. We replace the filter every year and have no stink, never had a 'splash up' into the filter (sits about five feet above the tank) and I don't hear any 'flow noise/air whistling' while pumping out.

My thought was to put a simple T between the filter and the tank, and on the new leg a simple ball valve that I can simply open before and close after the pump out to allow for an unobstructed air flow into the tank.

Thoughts? Am I overthinking the whole thing?
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Old 08-11-2019, 14:31   #2
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Re: Worth the effort? Extra black tank vent.

Sounds like a reasonable safety measure, to me. Not difficult, nor expensive, so why not?

Good for your peace of mind.

Cheers.
Paul.
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Old 08-11-2019, 14:33   #3
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Re: Worth the effort? Extra black tank vent.

You're not over-thinking it, but teeing into the vent line to add a ball valve isn't the solution. 99% of vent line blockages occur in two places--the vent thru-hull and the other end of the vent line...the vent fitting on the tank and that end of the vent line caused by waste splashing into it, which can happen even if the tank is only half full when the boat gets tossed around--a problem that a tee in the vent line wouldn't prevent. So IMO the best solution is a second vent line and new vent thru-hulls that'll let you put a hose nozzle against 'em to backflush the vent lines every time you wash the boat and/or pump out.

Why new thru-hulls? Boat builders use the same thru-hull for all tank vents--water, fuel and waste. They're designed to keep sea water out of the fuel and water tanks, so they allow barely enough air flow to function. Even dust, pollen and tiny insects can easily clog the tiny slit or pinholes and there's no way to keep 'em flushed out. It doesn't matter whether a little sea water can splash into a waste tank vent, so open bulkhead or "mushroom" thru-hulls are a much better choice for a waste tank vent.

A second vent line has other benefits: it allows better air exchange with the gasses in the tank, helping to keep the tank aerobic and maybe even eliminating the need for a filter. And it's not hard to do, thanks to a li'l gizmo called the Uniseal UNISEAL

You're welcome to give me a shout via email if you'd like to discuss in more detail specific to your tank and venting than is practical in a forum.

--Peggie
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Old 09-11-2019, 20:37   #4
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Re: Worth the effort? Extra black tank vent.

Iím surprised Peg didnít say to can the filter, they cause more problems than they solve.
Iím thinking she didnít notice you said you have one.
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Old 09-11-2019, 21:04   #5
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Re: Worth the effort? Extra black tank vent.

Quote:
Originally Posted by peghall View Post
You're not over-thinking it, but teeing into the vent line to add a ball valve isn't the solution. 99% of vent line blockages occur in two places--the vent thru-hull and the other end of the vent line...the vent fitting on the tank and that end of the vent line caused by waste splashing into it, which can happen even if the tank is only half full when the boat gets tossed around--a problem that a tee in the vent line wouldn't prevent. So IMO the best solution is a second vent line and new vent thru-hulls that'll let you put a hose nozzle against 'em to backflush the vent lines every time you wash the boat and/or pump out.

Why new thru-hulls? Boat builders use the same thru-hull for all tank vents--water, fuel and waste. They're designed to keep sea water out of the fuel and water tanks, so they allow barely enough air flow to function. Even dust, pollen and tiny insects can easily clog the tiny slit or pinholes and there's no way to keep 'em flushed out. It doesn't matter whether a little sea water can splash into a waste tank vent, so open bulkhead or "mushroom" thru-hulls are a much better choice for a waste tank vent.

A second vent line has other benefits: it allows better air exchange with the gasses in the tank, helping to keep the tank aerobic and maybe even eliminating the need for a filter. And it's not hard to do, thanks to a li'l gizmo called the Uniseal UNISEAL

You're welcome to give me a shout via email if you'd like to discuss in more detail specific to your tank and venting than is practical in a forum.

--Peggie

The standard little vent you speak of is a flame arrestor and is inappropriate for a black water tank vent.

Instead of a manual ball valve, think of a check valve arranged normally closed but opening on partial vacuum in the tank.
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Old 09-11-2019, 22:27   #6
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Worth the effort? Extra black tank vent.

I have a Tmq electric head that pumps into my waste tank, my thoughts are that if there is too much vacuum for the breather then it will suck air back through the toilet bowl? And this should cause no problems.
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Old 10-11-2019, 07:12   #7
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Re: Worth the effort? Extra black tank vent.

I noticed...but I also noticed that he said it's about 5' above the tank, which means his tank is buried so deep in his bilge that his vent line is long, vertical and prob'ly not straight either. Sometimes a filter or aeration can be the only solutions. Hopefully he'll accept my offer to brainstorm it one-on-one.


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Old 10-11-2019, 18:38   #8
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Re: Worth the effort? Extra black tank vent.

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I have a Tmq electric head that pumps into my waste tank, my thoughts are that if there is too much vacuum for the breather then it will suck air back through the toilet bowl? And this should cause no problems.
That was my thought as well, just have someone flushing the toilet while you pump, if even that is required.
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Old 10-11-2019, 19:30   #9
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Re: Worth the effort? Extra black tank vent.

I donít think you even need to flush as there is only a plastic impeller that doesnít block free flow. A mincer blade, and a one way flapper valve that free flows outward
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Old 10-11-2019, 20:27   #10
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Re: Worth the effort? Extra black tank vent.

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I have a Tmq electric head that pumps into my waste tank, my thoughts are that if there is too much vacuum for the breather then it will suck air back through the toilet bowl? And this should cause no problems.

It can definitely cause problems. For one thing, it would have to pull air through the slit in the joker valve (assuming that the joker valve isn't so worn that the slit has become a hole). For another, anyone who'd take that approach to sanitation system maintenance isn't likely to keep the toilet discharge line free of sea water mineral buildup that can reduce the diameter to less than 1/2" or keep the vent free of blockages. And flushing the toilet while you try to pump out would just push water through the line through which you're trying to PULL air!



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Old 10-11-2019, 21:39   #11
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Re: Worth the effort? Extra black tank vent.

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Originally Posted by peghall View Post
It can definitely cause problems. For one thing, it would have to pull air through the slit in the joker valve (assuming that the joker valve isn't so worn that the slit has become a hole). For another, anyone who'd take that approach to sanitation system maintenance isn't likely to keep the toilet discharge line free of sea water mineral buildup that can reduce the diameter to less than 1/2" or keep the vent free of blockages. And flushing the toilet while you try to pump out would just push water through the line through which you're trying to PULL air!



--Peggie
Thanks Peggie
The tmq electric only have a flapper valve, not a joker valve like the manual pump ones
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Old 15-11-2019, 19:12   #12
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Re: Worth the effort? Extra black tank vent.

Hello .Peggy has the right idea . Definitely do not put any fittings in there that will cause any restriction to airflow, such as checks valves or ball valves. Big problem with having two vent outlets on a waste tank is , you will have times of a breeze blowing, might be sitting on the dock or around the back deck only to start smelling waste, and as the breeze blows through one vent and push it out the other causing odour . The best solution to is to enlarge the size of the vent . Most new mid-size and larger boats come with inch-and-a-half venting systems now ,as it is the top priority for most waste systems to work properly and be happy.
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Old 15-11-2019, 20:05   #13
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Re: Worth the effort? Extra black tank vent.

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And flushing the toilet while you try to pump out would just push water through the line through which you're trying to PULL air!



--Peggie
On my electric toilet there is one direction to fill the bowl and one direction to flush. So if the vent line was stuck, it would simply suck whatever water was in the line between the toilet to the tank (it dumps into the top of the tank) and then suck air. I'd be very surprised if the tank collapsed before the joker valve allowed air to be sucked through it, I would imagine far more pressure would be needed for the former than the latter? That said, the constriction from saltwater and urine reacting is a real thing for sure, I ended up just replacing my lines rather than chip it out (they were no longer impervious to odor anyway).
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