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Old 09-12-2020, 07:36 PM   #1
Insertfubnyforumname
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Question about grey and black tank vents

Hey guys, super newbie here. I couldn’t find a direct answer online for this so I figured I’d ask you guys. I was checking over all the plumbing in my Bullet 198rbs recently. A long time RVing friend told me that campers always have 2 or more roof vents, one for each of the grey and black tanks installed. I can only fine one vent on the roof and when I follow it down no other pipes seam to merge before going into the floor, I haven’t crawled under to look at the tanks underneath yet. My question is, do some companies like keystone merge these two vents on smaller units like mine? Or is it possible that the grey tank is venting somewhere else entirely and not in the roof? Sorry for being a noob but I appreciate any insight.
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Old 09-12-2020, 07:49 PM   #2
mikec557
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Originally Posted by Insertfubnyforumname View Post
Hey guys, super newbie here. I couldn’t find a direct answer online for this so I figured I’d ask you guys. I was checking over all the plumbing in my Bullet 198rbs recently. A long time RVing friend told me that campers always have 2 or more roof vents, one for each of the grey and black tanks installed. I can only fine one vent on the roof and when I follow it down no other pipes seam to merge before going into the floor, I haven’t crawled under to look at the tanks underneath yet. My question is, do some companies like keystone merge these two vents on smaller units like mine? Or is it possible that the grey tank is venting somewhere else entirely and not in the roof? Sorry for being a noob but I appreciate any insight.
I don't know your unit specifically but I can say it is not a hard and fast rule for 2 or more roof vents. On a Grand Design I had two gray and one black vents combined in the wall and only one roof vent.

On my present Cougar I have a black and gray tank at the rear of the TT and each has a roof vent. But I also have an additional gray for a kitchen at mid length, with a separate pull gate, and it does not have a roof vent, though I think there is a vent under the kitchen counter.

You might take a look under your bathroom counter, near the sink.
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Old 09-12-2020, 07:59 PM   #3
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In place of a regular open vent on the roof, sometimes they install an air admittance valve in a cabinet that replaces the need for a vent to the roof.
https://www.plumbingsupply.com/how-a...-are-used.html
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Old 09-12-2020, 08:02 PM   #4
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Look under your sinks for something similar to the above picture, this is typically what they use for sink/grey vents.
Odds are the single vent is for the toilet.
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Old 09-12-2020, 10:39 PM   #5
Insertfubnyforumname
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In place of a regular open vent on the roof, sometimes they install an air admittance valve in a cabinet that replaces the need for a vent to the roof.
https://www.plumbingsupply.com/how-a...-are-used.html
Wait but I thought AAVs were only to equalize pressure to prevent siphoning in a trap. Isn’t the purpose of the vent from the tanks to also dispose of sewer gas build up? Is that not an issue on the grey tank?

Again sorry not used to camper plumbing :-P
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Old 09-12-2020, 10:42 PM   #6
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Look under your sinks for something similar to the above picture, this is typically what they use for sink/grey vents.
Odds are the single vent is for the toilet.
You’re correct I found 2 AAVs next the the p traps. Does this mean that grey tanks don’t create gasses that need disposal since those AAVs should be one way valves for equalizing pessure?
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