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Old 11-21-2020, 06:18 PM   #1
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Gray tank layout ??

I posted a few weeks ago about not being able to drain my gray tank. Well, after back flushing it with a hose and snaking it, I got some drainage ... but not a full 40 gallons. The tank sensors show 2/3 full now. I know not to completely trust the sensors, but I believe there is still maybe 20 gallons still in there.

Does anyone out there have a layout of the gray tank(s) in a 2007 Dolphin?? And any ideas for my next attack?

Thanks for any help.

Karl
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Old 11-21-2020, 11:05 PM   #2
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Dolphin Diagrams.pdf

This is for the 5342 for 2004. It may at least give you a starting point.
you're correct about not trusting the sensors. on my 5342 I have to raise the front of the MH to get the last few gallons out of the gray tank.
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Old 11-22-2020, 10:05 AM   #3
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It's possible that something is blocking the drain outlet from inside the tank, specifically, the remnant of the holes cut in the top for vent/drain pipes. This has happened to several others who have various brands of motorhomes. Those disks fall into the tank and, over time, can wash down toward the outlet where they eventually block the passage.

Not saying that's your issue, but it is one reasonable possibility. Back flushing like you did could dislodge the piece, but it may just float back into position as the water drains out.
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Old 11-22-2020, 10:41 PM   #4
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Also check the kitchen and bathroom sink air admittance valves. They have a spring and rubber seal inside the spring can rust and seal dry out over time. I had this problem in my previous class C and it caused the gray tank to drain slowly. Not sure where they are on the Dolphin but often under the sinks.
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Old 11-23-2020, 02:11 PM   #5
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Thanks Steve. The schematics will be very useful! Karl
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Old 12-22-2020, 11:55 AM   #6
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I may be late to replying, but on my 2007 Dolphin, the gray tanks drain very slow at the end. I have left mine open for 20-30 minutes before to get the last several gallons out..
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Old 12-22-2020, 12:04 PM   #7
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Quote:
Originally Posted by Piggy2 View Post
I may be late to replying, but on my 2007 Dolphin, the gray tanks drain very slow at the end. I have left mine open for 20-30 minutes before to get the last several gallons out..
It's been a month......hopefully OP has figured it out
Maybe OP will response with results
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Old 12-22-2020, 11:41 PM   #8
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The gray tank draining continues to be a pain. I took the rig out of storage this week and tried again. I have back flushed and snaked it twice now. I believe there is no blockage, just a bad drain location, possibly on the side of the tank rather than the bottom. If the rig is lifted a bit higher on the passenger side, more draining happens, but still quite slow. My tank sensors still show over half full, but i don't believe them anymore. Possibly they are caked with tank scum or possibly some type of electronic failure in the monitor.

Bottom line ... I think all is good. Thanks to all the helpful input from the forum folks. Your experiences are really helpful.
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Old 12-23-2020, 09:59 PM   #9
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Quote:
Originally Posted by Karlos View Post
The gray tank draining continues to be a pain. I took the rig out of storage this week and tried again. I have back flushed and snaked it twice now. I believe there is no blockage, just a bad drain location, possibly on the side of the tank rather than the bottom. If the rig is lifted a bit higher on the passenger side, more draining happens, but still quite slow. My tank sensors still show over half full, but i don't believe them anymore. Possibly they are caked with tank scum or possibly some type of electronic failure in the monitor.

Bottom line ... I think all is good. Thanks to all the helpful input from the forum folks. Your experiences are really helpful.
Dump lines do come out the side vs bottom

Even with tilting the RV the tank should drain fairly quickly

You should check that the Vent Line is CLEAR and unobstructed
*Remove roof cap and run garden hose down the line with drain valve open
Vent is sized at minimum to be capable of allowing AIR in/Air out at same rate liquids go out/in
**Plus the AAVs on sink drain lines add to the air in volume when dumping tank ---they are there primarily to prevent 'P' traps from getting sucked dry due to negative pressure in line when dumping tank. Neg pressure pulls them open so Air goes in downstream of 'P' traps.
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Old 02-05-2021, 11:44 PM   #10
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Open the tank drain and turn on the kitchen fauct. You will see if it is draining. My tank sensors NEVER show empty even when tanks are empty.
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