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Old 10-25-2018, 08:13 AM   #1
Livin salty
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M.O.C. #22108
Black tank flush

So as I performed my first tank dump this morning I was stumped by the black tank flush. I do have experience with it on another fiver but the 3931fb has 2 grey and black tanks. So my question is which tank is it “flushing”? Does it run to both at the same time and if it does I am assuming that I would need to have both black tanks open while conducting this flush. Or does it just flush the bedroom black tank leaving the downstairs one stanky?
If anyone has experience with this I would love to hear from you as we are pulling out this Sunday and putting it away for the Winter so I would like to get it flushed out as good as possible. Thank you
DIrk
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Old 10-25-2018, 08:39 AM   #2
K0LCB
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M.O.C. #13395
I think I remember someone saying only one tank had flush. Empty both tanks, run flush for a minute, open one tank at a time to see
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Old 10-25-2018, 10:19 AM   #3
Mikendebbie
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M.O.C. #21044
black tank flush

The 3931FB (similar to my 3921FB) has two black tanks and two gray tanks.
I leave both gray tank valves open while we are camped. Some folks close the gray valves a day before leaving with the intent of using the gray tank contents as a final flush for the hose after the black tanks are emptied. I never can remember to close the gray valves the night before leaving, plus I just do not want to "hold" the contents of a full bath tub in the tank...probably just a mental thing for me (bad experience years ago, forgot to drain the gray, it overfilled, long story)- but I just don't want to fill my gray tanks. We never dry camp.

There are two hose connections in the very bottom of the convenience center. The one on the left is black tank flush for the front (full bath) black tank, and the other one is flush for the rear tank serving the half bath room. I hook up hoses to both flush connections. I open both valves and let the contents run out until it is a slow drip, then close both black valves and turn on the water hoses. On my unit - the front black tank (half bath) drains and flushes like a champion! Good gravity flow! I will close the valve and let it fill for a minute or so then open the valve and let it drain. Close to fill and open to drain again. I have a clear plastic elbow coming off the RV drain so I watch the stuff coming out until it runs "clear". I will alternate between the front tank and the rear tank opening the valve on one while the other tank fills.

My rear black tank does not gravity-drain as nice as the front tank. The half bath tank empties with a GUSH...the other tank - not so much, decent flow but never a gush! It's been this way since we got the unit in January 2018. I suppose it has to do with the routing of the sewer pipe. I have to spend more time flushing and monitoring the front black tank. Eventually it runs "clear".
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Old 10-25-2018, 10:24 AM   #4
1retired06
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Quote:
Originally Posted by Mikendebbie View Post
The 3931FB (similar to my 3921FB) has two black tanks and two gray tanks.
I leave both gray tank valves open while we are camped. Some folks close the gray valves a day before leaving with the intent of using the gray tank contents as a final flush for the hose after the black tanks are emptied. I never can remember to close the gray valves the night before leaving, plus I just do not want to "hold" the contents of a full bath tub in the tank...probably just a mental thing for me (bad experience years ago, forgot to drain the gray, it overfilled, long story)- but I just don't want to fill my gray tanks. We never dry camp.

There are two hose connections in the very bottom of the convenience center. The one on the left is black tank flush for the front (full bath) black tank, and the other one is flush for the rear tank serving the half bath room. I hook up hoses to both flush connections. I open both valves and let the contents run out until it is a slow drip, then close both black valves and turn on the water hoses. On my unit - the front black tank (half bath) drains and flushes like a champion! Good gravity flow! I will close the valve and let it fill for a minute or so then open the valve and let it drain. Close to fill and open to drain again. I have a clear plastic elbow coming off the RV drain so I watch the stuff coming out until it runs "clear". I will alternate between the front tank and the rear tank opening the valve on one while the other tank fills.

My rear black tank does not gravity-drain as nice as the front tank. The half bath tank empties with a GUSH...the other tank - not so much, decent flow but never a gush! It's been this way since we got the unit in January 2018. I suppose it has to do with the routing of the sewer pipe. I have to spend more time flushing and monitoring the front black tank. Eventually it runs "clear".
Same with our 3910. Half bath flushes easier, sits right over the black tank, full bath is not.
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Old 10-25-2018, 09:11 PM   #5
Livin salty
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M.O.C. #22108
Thanks guys. Sometimes I get stuck on stoopid and get love past. I will try the one valve at a time and see what happens. Hopefully no bio suits are needed.
Maybe that why I was so scared and didn’t do anything lol. Enjoy ya’lls evening
Dirk
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Old 12-27-2018, 04:31 PM   #6
footz1941
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M.O.C. #21057
Close both grey valves before opening black water valve. No cross contamination Open black water and let it run until clear. Close valve and set alarm on my phone for 10 minutes so I do not get distracted then open black water again Usually do twice Shut off rinser and open grey valves. Have did this for years with no problems and using no chemicals. Only do this when hooked to sewer not when using a busy dump station
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