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Old 04-14-2014, 10:59 AM   #1
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Does a grey water tank need to be vented?

We're replacing our toilet with a composting one. Our '66 Safari only has the combined black/grey water tank. Since we're removing the black water component, do we still need to vent the tank through the top of the trailer? It will effectively be vented through the drain pipe vents...right?


Also, do we really need to vent the drain pipes? Does the vent do anything other than prevent the gurgling? The only thing connected to the drain is a dish sink. We removed the bath sink and shower. Would a tank full of soapy water really need venting?


If I could remove the vertical piping I could make the interior SO much cleaner!


Thanks,
Karen
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Old 04-14-2014, 11:03 AM   #2
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Any time you let water out of a tank, you have to let air back in at the same time to ensure good flow. That's what the vents do. So the answer is, yes, you still need the vents on the tanks and drain pipes.
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Old 04-14-2014, 12:00 PM   #3
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Or any time you want to put water into the tank, you must let the air out. That is what the vent does, as it is above the tank inlet.

Bill

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Any time you let water out of a tank, you have to let air back in at the same time to ensure good flow. That's what the vents do. So the answer is, yes, you still need the vents on the tanks and drain pipes.
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Old 04-14-2014, 12:10 PM   #4
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The storage tanks need to vent pressure and gases.

The drains need vents to prevent not on only gurgling, but siphoning the drain traps enough so dangerous gases from the tanks cannot come back up through the drains. I noticed Airstream uses an air admittance valve near the shower for this purpose in our trailer. You might check on them, if they're legal, and especially proper and safe installation.
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Old 04-14-2014, 12:49 PM   #5
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Also drains flow much faster with vents. Replaced my bath sink without a built in vent in the sink - when full took what seemed like 5 min.s to empty - went back and added a inline vent beneath the sink and it now flows right out!
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Old 04-14-2014, 01:06 PM   #6
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Also drains flow much faster with vents. Replaced my bath sink without a built in vent in the sink - when full took what seemed like 5 min.s to empty - went back and added a inline vent beneath the sink and it now flows right out!


Silver Hawk,
I think you're getting to the heart of my question. What type of vent did you use? Do you still have the big, vertical pipe that goes through the roof?


If I have a vent in the grey tank, and a vent in the sink, wouldn't that do the trick? The only water used in the trailer is in the single sink. The fewer exterior penetrations, the better!


Thanks,
Karen
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Old 04-14-2014, 01:54 PM   #7
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Quote:
Originally Posted by kirkland1833 View Post
We're replacing our toilet with a composting one. Our '66 Safari only has the combined black/grey water tank. Since we're removing the black water component, do we still need to vent the tank through the top of the trailer? It will effectively be vented through the drain pipe vents...right?


Also, do we really need to vent the drain pipes? Does the vent do anything other than prevent the gurgling? The only thing connected to the drain is a dish sink. We removed the bath sink and shower. Would a tank full of soapy water really need venting?


If I could remove the vertical piping I could make the interior SO much cleaner!
If the tank you are referring to is the original one, it is only a black tank. Grey water in that era went straight to the ground, albeit through the same outlet fitting as the black water did.

Thanks,
Karen
Karen,
If the tank you are referring to is the original one, it is only a black tank. Grey water in that era went straight to the ground, albeit through the same outlet fitting as the black water did. Grey water tanks from the factory didn't generally start until 74.
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Old 04-14-2014, 02:51 PM   #8
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Karen,
If the tank you are referring to is the original one, it is only a black tank. Grey water in that era went straight to the ground, albeit through the same outlet fitting as the black water did. Grey water tanks from the factory didn't generally start until 74.


Colin,
Yes, it's a black tank. But we had some work done on it and they re-plumbed the sink to dump into the black tank. We're removing the toilet, so the tank will only hold grey water.




I've been poking around and found reference to Air Admittance Valves to vent the drain. If I install one at the sink and have a vent in the tank, that should do the trick, right?


We don't want to have any full height cabinets in our trailer, so I really want to eliminate the ceiling vents. Can the tank vent be routed out the rear of the trailer?


Thanks!
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Old 04-14-2014, 03:32 PM   #9
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Colin,
Yes, it's a black tank. But we had some work done on it and they re-plumbed the sink to dump into the black tank. We're removing the toilet, so the tank will only hold grey water.




I've been poking around and found reference to Air Admittance Valves to vent the drain. If I install one at the sink and have a vent in the tank, that should do the trick, right?


We don't want to have any full height cabinets in our trailer, so I really want to eliminate the ceiling vents. Can the tank vent be routed out the rear of the trailer?


Thanks!
Air Admittance allows air in to the drain plumbing to allow water to flow better, but they to not let air/fumes out of the tank…………which is what you need. The top of the tank must be vented outside somehow, either through the roof, or perhaps a vent through the side of the trailer, above the tank. Remember, methane is lighter than air, so it rises.
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Old 04-14-2014, 04:16 PM   #10
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Thanks, everyone! I feel like I have a plan now. I will install an AAV along with the sink, and I'll vent the tank through the rear of the trailer.


I really appreciate all of the input!
Karen
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Old 04-14-2014, 06:40 PM   #11
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Also, if the sink is near the storage tank and the drain line is large enough you may not need to ventilate with a vent pipe or air admittance valve. There isn't enough water coming from the sink and into the drain line to siphon out the trap. Our bath sink is maybe four feet from the tank and has no sink vent.

There are state plumbing codes for length and size of pipe for this type venting, and rv's probably have their own code if you wanted to research it.

But the tank still needs its own vent pipe (not an air admittance valve).
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Old 07-08-2017, 07:34 PM   #12
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two grey tanks

This tread is old but I can't seem to find an answer to my questions in previous treads. To all you plumbing expert out there, here are a few question that this neophyte cannot find answer:

1) If I install two grey tanks that are contiguous and at same level, how do I install a link between the two. What size of fittings and do I need a slope between pipes. I intend to have drains connect under the belly pan.

2) The shower pan would be directly on top of one of he grey tanks. Can it be fitted directly without a p trap? Or do I need to raise my floor?

3) Can the two grey tanks share the same vent? Meaning, can my second grey tank would not have a vent pipe but by being connected to the first grey tank, which would have a vent, it would be sufficient.

Apologies if these questions are silly... The learning curve is steep... :-)
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Old 07-08-2017, 07:52 PM   #13
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Quote:
Originally Posted by Juliec View Post
This tread is old but I can't seem to find an answer to my questions in previous treads. To all you plumbing expert out there, here are a few question that this neophyte cannot find answer:

1) If I install two grey tanks that are contiguous and at same level, how do I install a link between the two. What size of fittings and do I need a slope between pipes. I intend to have drains connect under the belly pan.

2) The shower pan would be directly on top of one of he grey tanks. Can it be fitted directly without a p trap? Or do I need to raise my floor?

3) Can the two grey tanks share the same vent? Meaning, can my second grey tank would not have a vent pipe but by being connected to the first grey tank, which would have a vent, it would be sufficient.

Apologies if these questions are silly... The learning curve is steep... :-)
Hi

Might be better to start a new thread ....

1) Multiple sewer tanks are not a real good idea. When hooking them "bigger is better". 3" is not a bad starting point.

2) If you run straight into the tank, it will "burp" back into the shower. That's generally not a nice thing. Even the gray tank gets a bit stinky after a while.

3) You can connect both tanks to the same vent. Simply remember that the vent must be at the high point in each tank. Usually this is done with a pipe from each tank going into a Tee and then into the vent.

Yes, there are a few other things to watch out for (setting up the drains ...).

Bob
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