Black Tank for water with compost toilet

[MarkC]

Could I fill the black tank through the wash down port.  Then drain into a container.   And, pump into water tank through boondock port at rear of trailer?

[Mike and Carol]

Assuming a composting toilet…

There is a backflow valve in the line for the black tank flush and the flush line enters the black tank near the top, so that won’t work.  The only other way is through the black/gray sewer hose that exits at the rear of the trailer.  Not very sanitary. Finally, I’m sure the plastic used in the black tank is not drinking water safe.

I would say no.  Mike

[Frank C]

The black tank drain valve and gray tank drain valve both share the common drain pipe in the Ollie.   The drain valves do not seal perfectly, so there’s a risk of cross over leakage/contamination between those two tanks.  I wouldn’t use the black tank for fresh water unless it was completely isolated from the gray tank.  And on Olivers with the composting toilet, I’m not sure if Oliver still cuts the hole in the top of the black tank where the toilet flange is installed with the flush toilet option.   There may be a 3” diameter hole on the top of the black tank, even with the composting toilet, since Oliver does try to make it easy to switch from one toilet option to the other. 

[John E Davies]

The upper black tank hole is plugged when there is a NH installed, no worries there. ABS can be used for potable water, the main drawback is it is never to be installed in direct sunlight, not a problem in an Ollie. By RV CODE you should not use the black tank, in reality it would work fine, as long as you disconnect it from the main 3" waste pipe under the front dinette seat, and cap off the tank outlet tank. Install a PEX drain line with shutoff valve and also a BIG PEX overflow pipe from the top of the tank, exiting out the bottom hull. And be sure to go under the bath sink and disconnect and cap the 1 1/2" black tank sewer vent, otherwise the two systems are still physically connected. While you are under there, cap off the fresh water line going to the toilet, so you don't have to keep winterizing that unused section of pipe.

I have been thinking about this for five years but never did it. Please go ahead and post pics, we like research and development pioneers here. 😉

Small projects tend to get big in a hurry when you figure out all the angles.

https://westernrooter.com/abs-vs-pvc-pipe/

John Davies

Spokane WA

[VBistro]

I hadn't thought about using the black tank for fresh water, but I *did* procure everything I need to use the black tank as extra gray storage.  Most places we boondock have water nearby that we can filter with a filtering jerrycan and pump into the fresh tank in boondock mode, but I often find ourselves butting up against gray tank limits.

If you haven't see this yet, it's clever!
 

 

[SeaDawg]

In a few words, don't do it. Grey water fine.

Fresh water could be easily contaminated, and the black tank is not rated for potable water.

 

[NCeagle]

On 8/2/2022 at 2:04 PM, Frank C said:

...And on Olivers with the composting toilet, I’m not sure if Oliver still cuts the hole in the top of the black tank where the toilet flange is installed with the flush toilet option.   There may be a 3” diameter hole on the top of the black tank, even with the composting toilet, since Oliver does try to make it easy to switch from one toilet option to the other. 

Just an fyi that obviously may change from trailer to trailer and year to year:

We have hull 688 (2020) with the composting toilet option out of the factory.  Although the hole is there in the fiberglass floor under our Nature's Head, our black tank has no drilled holes on top - or anywhere else.  It is also properly vented so you can fill it through the outside port (I use it for extra grey water storage only).  

[John E Davies]

3 hours ago, NCeagle said:

  It is also properly vented so you can fill it and empty it through the outside port (I use it for extra grey water storage only).  

How do you empty it through the outside port? Or was that a typo?

FYI if you overfill it, it will flood the bathroom, just like the main grey tank, ultimately coming out over the top of the door sill. Do you pump out of a bucket to keep track?

John Davies

Spokane WA

[NCeagle]

On 8/3/2022 at 9:56 AM, John E Davies said:

How do you empty it through the outside port? Or was that a typo?

FYI if you overfill it, it will flood the bathroom, just like the main grey tank, ultimately coming out over the top of the door sill. Do you pump out of a bucket to keep track?

John Davies

Spokane WA

Hey John, yes that was a typo.  I only fill it through the outside port.  I avoid overfilling it using a stopwatch and the See Level monitors.  I'll run it for 2.5 minutes because my pump runs pretty close to 5 gallons per minute.  Then I'll check my grey and black See Level monitors and it confirms about 12-13 gallons into the black tank.  I don't push it to 15 gallons for fear of pushing water up the vent and into places it doesn't belong.  Yuck.  🙂