Dump Black Tank at end of Camp Session or wait till 3/4 full

Probably silly question, but can't find it directly answered. If camping for 2 days and then going to be done for 3-4 weeks should I dump the black tank, even if only minimally full or are you supposed to wait more till 3/4 full and let it sit for weeks to months at a time for that to occur?

Fill with fresh water until 3/4 full, then dump. Do the same with the gray tank and you'll never have any odors.

HappyWanderer said:

Fill with fresh water until 3/4 full, then dump. Do the same with the gray tank and you'll never have any odors.

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X2

I have the mrs stand by the tank monitor and let me know when it's 3/4 full while I hold the foot flush pedal and run water in the shower. Once their 3/4 full, I stop and go dump. after dumping, I put a few gallons back in each and add a tablet to the black tank.

HappyWanderer said:

Fill with fresh water until 3/4 full, then dump. Do the same with the gray tank and you'll never have any odors.

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I full time so that's no longer and issue but I had a dump station at home.

Either what HW said or.. what I did.. Last 60 odd mile trip Id' dump (As HW suggests) then fill with I forget if it's a half cup or full cup of Calgon Watersofterner (Dry or wet) Dawn Regular (NOT antibacterial) and about 1/3 tank water.. Then dump again at home.. Nice clean tank.

NOT a silly question!  An important thing to know.  Correct answers have been posted.

I'm not going to argue against any of the posts or the "common knowledge" about not dumping with low levels.....
but I have noticed something that puts a bit of a question mark in all of that idea of needing a full tank to pull the stuff out..

A long time ago at home I did some experimenting.  This was done when the rig was still fairly new and at that point I had always waited till more than 3/4 full to dump.... I've dumped, rinsed, and repeated a few times trying to really get a clean tank.  I really can't answer why because I don't really care if it's spic n span...it's a black tank.... except that I'm bugged by having level lights that don't work.... yes, it's a psychological issue I know....  Anyway through a clear elbow connector ... I've noticed that the water will run relatively clear through most of the dump, then lots of remaining stuff will come out as the flow slows to just the wash across the floor of the tank.  Refill, and this repeats.  I've done it several times in a row and even after several extremely clear dumps, still there will be a surprising amount of paper and stuff coming out at the end...not so much during the fast part of the dump but at the end, even after 3-4 clear rinse dumps or more.
So
I'm guessing what happens is that during the full part of the dump when the water is really rushing out it's probably mostly just a vortex pulling from the upper and central regions of the tank's space and the region of liquid with the solids settled towards the bottom are more or less bypassed until the water level slows enough to stop the vortex and just slowly wash across the tanks floor.... then and only then does it pick up the stuff from the tank floor.

Based on these observations and my guess as to what's happening, I personally don't figure it's the end of the world to do a "short" dump now and then....as long as whatever in there is still mostly liquid.  I wouldn't do it if the tank level was nearly empty already,but half, or maybe 1/4 now and then maybe... I always try to wait till full or close, but sometimes that just doesn't work out....But in the rare times that I do feel like my dump was a bit early, I'm extra careful about adding lots of clear water and maybe some detergent right away to the freshly dumped tank to prime it....and when possible will try to do a rinse dump fairly soon after... 

IMHO - this is almost always overthought.  I run my black flush'ing thing every time until it runs clean.  Makes the guages almost work

That said, on prior units that didn't have this I was fine....for years. 

Use lots of water in the toilet - you'll be fine.....

As to when you dump - - when you want to.  No reason to rush or worry if it sits with "stuff" in it.

-Kyle

-Kyle

On occasion we've used our camper as a guest house and I have no way to dump at home. The black tank might only get used a few times over a weekend and it might be 3 or 4 weeks until our next outing. I just make sure there's plenty of water in there to keep things moist. There should not be any stink - unless the wind blows just right across the vent, I suppose, but that's no different than the house. Dumping would be ideal but I don't think it's a mistake or potential disaster to leave it for a few weeks at a time.

CincyGus said:

X2

I have the mrs stand by the tank monitor and let me know when it's 3/4 full while I hold the foot flush pedal and run water in the shower. Once their 3/4 full, I stop and go dump. after dumping, I put a few gallons back in each and add a tablet to the black tank.

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I have a similar procedure, when we get home I add water to get both tanks to 3/4 or more, then dump both. Then I repeat, sometimes twice.
Then Before I park it I add atleast a couple gallons of water to each tank to - hopefully - keep the seals from drying out and also prevent the "solid blockade" I've read about in other discussions.

Brad:

Very interesting theory!  If I understand correctly, a good flush of 5 - 10 gal of fresh water after draining will more effectively "dump" the tank than waiting until it is ⅔ full or adding 15 gal to the tank before dumping.

My limited experience is similar to yours.  That first black rinse usually contains more "stuff".

grashley said:

Brad:

Very interesting theory!  If I understand correctly, a good flush of 5 - 10 gal of fresh water after draining will more effectively "dump" the tank than waiting until it is ⅔ full or adding 15 gal to the tank before dumping.

My limited experience is similar to yours.  That first black rinse usually contains more "stuff".

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Yeah...that's a great way to put what I was trying to get at.... well, the numbers depend on the tank size, but.....

I might change my "statement" to this...
using ballpark levels, nothing scientific.... based on what I have noticed, I'm thinking that filling my tank to maybe 1/4 level as a "rinse cycle" seems to get about the same amount of stuff out as filling it all the way full.