Gray tank & Black tanks

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2+1 for the road

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Sep 30, 2019
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Hi to all the experienced RV?s. We finally got house closed and are in our 5th wheel. So, I know to always keep black tank closed and only open when it needs to be emptied. But, what about gray tank? When in camp ground with sewer hook up can you leave gray tank open or should it be closed like black tank? I know this probably seems like a silly question but we are still in our learning curve.
 
2+1 for the road said:
Thanks. That will be better than having to empty every 4 or 5 days.
Click to expand...

That is not a silly question. I always left mine open. A day before I was going to empty the black tank, I'd shut the gray tank and let it fill up. Then I'd use that water to flush out the drain hose better known as the "Stinky Slinky".
 
I added a third, Valterra, bayonet gate valve (C) to the outlet of the wye where the black (B) and gray (G) tank drains converge.

I keep all three valves closed until dumping time.

At that time, open C and B and drain the black tank. When it has mostly stopped draining, close C and open G. That backflushes the black tank with a slug of gray water and loosens up a lot of other "stuff". Listen, and you can hear when the water stops moving as the tanks equalize.

Then, close G and open C and flush the backwash out of the black tank.

Repeat until the backwash runs, uh, clearish (grayish?), or until you run out of gray water.

Open all 3 to drain out whatevr is left, close all of them, disconnect, and clean up.

A Rhino or other drain hose with a clear elbow at the far end makes this a lot more easy to inspect the flow.

I first built something like this on our 88 Suncruiser from parts before the cool Valterra "repair" valve was a thing.

Here's a link to the valve:

https://www.amazon.com/Valterra-T58-Twist-On-Waste-Valve/dp/B000BGHYJS/



 
SLOweather said:
I added a third, Valterra, bayonet gate valve (C) to the outlet of the wye where the black (B) and gray (G) tank drains converge.

I keep all three valves closed until dumping time.

At that time, open C and B and drain the black tank. When it has mostly stopped draining, close C and open G. That backflushes the black tank with a slug of gray water and loosens up a lot of other "stuff". Listen, and you can hear when the water stops moving as the tanks equalize.

Then, close G and open C and flush the backwash out of the black tank.

Repeat until the backwash runs, uh, clearish (grayish?), or until you run out of gray water.

Open all 3 to drain out whatevr is left, close all of them, disconnect, and clean up.

A Rhino or other drain hose with a clear elbow at the far end makes this a lot more easy to inspect the flow.

I first built something like this on our 88 Suncruiser from parts before the cool Valterra "repair" valve was a thing.

Here's a link to the valve:

https://www.amazon.com/Valterra-T58-Twist-On-Waste-Valve/dp/B000BGHYJS/
Click to expand...

X's 2 on this.

By keeping the both Black and grey valve closed you reduce the chances of odors from the dump point entering the RV systems.
 
When a valve is open you expose your system to the entire campground sewer system with all its odors, sewer flies and malfunctions.  I don't mind doing something as simple as pulling a valve one or twice a week.
 
Odors from the sewer system can't get any further than the gray tank as long as the P-traps in the waste plumbing are working, meaning they have some water in them. Sometimes the traps get dry, though, especially in RVs that travel and then sit without use of all the plumbing. Water sloshes out of a P-trap while driving or parked at an tilt and it doesn't get replaced until somebody runs some water down the appropriate drain.

A good habit is to form your own P-trap in the waste drain hose that connects to the campground sewer.  Put something under the hose so that there is a hump in it, trapping some water on the RV side of the hump. A piece of fire wood, a stone, or even lop the hose back over itself.  Once the hose on the RV side of the hump fills with water, odors and flies can't travel up the hose, yet additional water will continue to flow over the hump.  It's ironic that those folks who make sure their sewer hose has a  nice level or downhill run are those who are most likely to get odors or sewer flies.
 
Thanks Gary, I never considered the smell issue with leaving it open, we are newbies after all. We have been at a RV park for about 2 weeks now and with just my husband and myself it wasn?t an issue. We kept it closed and opened on about day four to drain then closed it. But then, the teenage granddaughter arrived, lol, and with her showers it didn?t take long to fill up. That was the reason for the question. My husband said he would leave it open and close a day before we drain black tank so that?s what we are going to try for a couple weeks.

And thanks to everyone for their help and suggestions. I?m sure I?ll be back with plenty more.
 
Understand that leaving the gray drain open is no different than how the your waste plumbing works at home, i.e. always open to the sewer or septic system.  Your stick home relies on the P-traps to keep odors and flies out, just like the RV. However, RV park waste systems get a lot of abuse and aren't always well-maintained, so maybe the risk is higher.  If for no other reason because you visit a lot of them while traveling, so sooner or later you may hit a troublesome one. It's important to be aware that odors and flies are a possibility, so that you know what to do if the symptoms appear. Typically not a problem, though, so go ahead and enjoy the convenience of infrequent gray water dumps.
 
Think about your house. Do you have sewer smells in your house? The RV is no different. EXACTLY THE SAME. Leave the gray open. leave the black closed so not to make a poo pile in the tank. Not because of smells.
 
From actual experience, BOTH CLOSED until they need to be emptied, then gray flusheds out the line after black has been cleared first.
My experience was the park system backed up, were on a hill, but lower than some, but higher than the backup, so! When everyone uphill dumped theres it hit the back up and ended up partly filling the tub with someone else's **** literally!!
 
Conesus1 said:
From actual experience, BOTH CLOSED until they need to be emptied, then gray flusheds out the line after black has been cleared first.
My experience was the park system backed up, were on a hill, but lower than some, but higher than the backup, so! When everyone uphill dumped theres it hit the back up and ended up partly filling the tub with someone else's **** literally!!
Click to expand...

Thanks. That was a disturbing observation. I shall remember that forever, and always request an uphill site. ;)
 
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