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Old 09-18-2022, 11:42 AM   #1
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Galley gray tank - Open drain valve question

On a 5th wheel unit, some say leave the galley gray tank valve open, some say closed. Let's assume you are in the "leave the valve open" camp. Is there a likely risk of having black tank "stuff" flow into that gray tank while dumping the black, with the galley gray tank valve remaining in the open position?

In our daughter's instance, the galley gray tank valve is in a very awkward position, behind the skirting and under the kitchen slide. Opening it is a significant task, especially as we grow older and less flexible. It would be nice to have an electric valve on that tank, but the installation of such a valve would be a large and expensive undertaking.
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Old 09-18-2022, 11:57 AM   #2
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It all depends on how it's plumbed, but yes, there certainly is a chance the black water will flow into the grey tank. I occasionally do the opposite and let some grey water backflow into the drained back tank. Naturally the next question is: Is that a bad thing? And the answer is no. A little back water going into the grey tank will drain back out, and any small amount left behind will get washed out as the grey water flows out. They are both holding tanks and don't differ in how they handle waste, with only difference is the size of the drain valve.

Have you considered a less costly solution such as a cable actuated replacement valve kit?
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Old 09-18-2022, 06:17 PM   #3
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Water will flow downward faster than it could flow up into galley tank

And even if it would drain right back out cause the galley dump valve is open

They are Waste tanks.......grey/black especially galley all the same....waste

Biggest issue with leaving a dump valve open is the possibility of sewer flies setting up home inside your waste tank. Then they invite cousins and friends to join them. Sewer flies are tough to get rid of once established
*make a dip in the sewer that will hold water....'P' trap....that will prevent critters and sewage gasses from coming back into the RV
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Old 09-18-2022, 07:07 PM   #4
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I like your thoughts, Tom, and my "old" friend from the Monaco forum, Old-Biscuit.

First, you both supported my thinking that any up-flow into the galley tank might not be much, if any of a problem. A person could run the kitchen sink cold for a minute or two to "flush" it back out. Thank you!

Second, I've seen several sources that recommend the "P-trap" in the sewer hose to prevent fumes and critters from surfacing via the open valves and the roof vents. The only caveat I have there, is that personally, I would be lifting the hose while dumping the black to allow a good flushing of the hose with the gray. Otherwise, seems like there would be a pretty nasty buildup in that section of hose, over time. But it probably would be manageable.

Third, I hadn't thought about re-locating the valve pull device. Great idea. The only negative would be the need to get to the physical valve, itself, to install the replacement. But once in there, it shouldn't be oo big of a job. I replaced the black tank valve on our Dynasty several years back, and other than it being less fun than dancing or eating dessert, it wasn't all that bad. If I did go to the trouble if invading the belly, I might actually opt for an electrically operated dump valve, as most of the invasive work would already be done.

Thank you both! Great suggestions.
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gray tank, tank, valve

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