Dumping Black Tank

[sprehoda]

Is it better to dump the the black tank intermittently or to leave the valve open all the time?

Steve Prehoda

[bstark]

Another topic that gets lot's of to and fro's.

Dumping periodically is the prescribed method of black tank maintenance.

For those with the discipline to wait to the last flush before dumping will go the prize for the cleanest tank without additives or major flushing with fresh water.

For those of us who were loath to suffer the ire of a spouse whose butt got sprinkled when attempting to flush a late night biffy visit; our method was to wait until a few days of normal usage had occurred, and given our habits, gauging the amount within the tank to as close to full as we dared risk it, to then dump and back-flush efficiently guaranteeing us a trouble free number of years of usage without encountering the dreaded "black mountain of doom" immediately under the toilet drop.

Volume of flow is what carries the lumps out the hose and letting the tank fill before dumping does two things: it allows for normal bacterial action to begin breaking down paper and larger bits. It also creates a large surge of liquid going down through the gates where the exit piping is narrowest thus forcing larger stuff along in it's path.

Leaving the gate open does neither so the big stuff stalls and sits to eventually create a pile.

Leaving the valve open will work for just so long before that pile of hardened material that has built up under your toilet drop pipe demands attention and that can be a messy business.

Closing your grey tank valve a couple of days prior to leaving can also be a good thing to do so that you have the added waste water available to assist clearing a blockage at the black gate by alternatively closing your extreme end of pipe gate (if you haven't installed one, do so now) and opening the grey to have water from the grey push through the line and up into the black and perhaps dislodge a blockage back into the black tank to then try again.

That soapy grey water is also nice to have handy as the last stuff to go down your sewage hose to "clean" it of the nasty bits and pieces of your prior black tank dumping and flushing exercise.

[Willym]

What he said above.

[5thwheeler]

Yup

[terry and jo]

Closing your grey tank valve a couple of days prior to leaving can also be a good thing to do so that you have the added waste water available to assist clearing a blockage at the black gate by alternatively closing your extreme end of pipe gate (if you haven't installed one, do so now) and opening the grey to have water from the grey push through the line and up into the black and perhaps dislodge a blockage back into the black tank to then try again.

That soapy grey water is also nice to have handy as the last stuff to go down your sewage hose to "clean" it of the nasty bits and pieces of your prior black tank dumping and flushing exercise.

With regards to the above text in bold, that will depend on the various models and brands. In our 2010, the black tank is mounted above the grey tank, so I doubt that the water released from the grey tank will even go up into the black tank.

In the picture, it shows the upper tank in the raised portion of the frame as the black tank, into which the toilet dumps directly. The tank that is below it is the grey tank.

Directly behind the "raise" in the frame at the entry steps is the fresh water tank.

Terry

[terry and jo]

Rather than edit and risk messing things up, here is another picture of that same DRV frame, only from the opposite side. In this one, the fresh water tank is right in front and one can see the discharge line from the black tank running down toward the outlet.

Terry