[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.