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Old 06-28-2016, 09:37 PM   #21
Senior Member
Brand: Thor Motor Coach
Model: Axis 24.1
State: Florida
Posts: 612
THOR #4366
Keep the black tank closed until 2/3 to 3/4 full. Personal choice on the grey but we leave it closed until it needs dumped. They grey fills faster so it's more often. We also make sure the grey as at least half full when dumping the black as a hose pre rinse.

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Old 06-29-2016, 12:56 AM   #22
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bevedfelker's Avatar
Brand: Thor Motor Coach
Model: 2015 Vegas 24.1
State: Pennsylvania
Posts: 1,339
THOR #2601
As stated earlier, one reason to keep the valves closed is sewer gas. But another really important factor is if you keep the black tank open the fluids will drain as you flush and the solids will stay behind, build up, and harden. There needs to be lots of fluid in the black tank to push the solids out.

Generally what I do is wait until the black tank is more than 1/3 but less than 2/3 full. I empty the black tank first. Wait until the hose has drained. Then I close the black tank valve and pen the gray to flush out the sewer hose.

Generally the gray tank will be about 2/3 full and the black between 1/3 and 2/3 when I dump the tanks. After dumping I add a Walex Bio Black tank treatment pod and some water to the black tank after EVERY emptying.

Here is a link to my latest version of the manual. You can download as a MS Word file, or use the menu and download as a .pdf file.


Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)
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