Black water rinse question

[boyscout]

Not sure I understand why the discharge valve must be open? Obviously it has to be open sometime to drain the tank, however, thw black tank is vented thru the roof, just like a household system so there will never be pressure build up. If the dump valve is closed, and the tank flush pressurized, the tank will fill and effluent will use the only exit it has which is thru the roof vent.

The discharge valve doesn't ALWAYS have to be open while the black tank flush is flowing - in part to allow the partial fills that you've described - but it's really important to stay close and attentive when it's closed and black flush is flowing.

There are stories about people overfilling the black tank such that it flowed up the vent and onto the roof, as you confidently predict, but there are also plenty of stories -- more stories - about people overfilling it and rupturing the black tank. That's a very expensive result in more ways than one. A friend of mine ruptured his while he was lying underneath it and years later still looks uncomfortable when he tells the story.

[boyscout]

What you are saying makes a lot of sense and is much easier than filling the black tank from the toilet. They have to be vented or the tanks aren't going to drain. I wonder that the thinking is for the warning in the owners manual is for. Maybe their lawyer's wanted it to prevent service claims for stained roofs.

See my response to @Skiddy above. It's okay to close an empty tank and black-flush-fill it for six-eight minutes - I do it all the time. However if you get distracted and leave it flowing for a lot longer you risk rupturing the tank. That'll take a big bite out of your travel time and your wallet.

[mkevinmarshsr]

See my response to @Skiddy above. It's okay to close an empty tank and black-flush-fill it for six-eight minutes - I do it all the time. However if you get distracted and leave it flowing for a lot longer you risk rupturing the tank. That'll take a big bite out of your travel time and your wallet.

When I do the flush I go stand at my control panel to keep a check on the black tank level. Once it gets to 2/3 full I go open the valve. I figure if I'm standing at the panel monitoring the levels I won't get distracted by a squirrel and forget the task at hand.

[Sportsdad60]

(Raises hand sheepishly) I ruptured our BW tank when I overfilled it once. I got distracted.
The RV technician was able to repair the crack without dropping the tank with some sort of stuff that he said he'd used on other rigs with great success.

And the patched up BW tank it served us well for a year. We recently traded that 5th wheel for a new GD 3 weeks ago.

FYI, I time the water flow coming out of the hose into a 5 gallon bucket. I.E. if it takes if it takes 1 min to fill a 5 gallon bucket, I now can calculate how long to keep the water source running in order to reach1/2 tank full for flushing out.

I like the GEO method when we travel after being stationary for months at a time, so I typically put about 10 gallons of H2O and the GEO components in the BW tank before we hit the road. Then dump at the next destination.

[CM2020RS]

I use a flow meter on the hose for flushing the black tank. that way I can close the valve and let the water build up for a while without risk. as long as you know your and size you can fill it 1/2 to 3/4 of the way for a good final flush.

[CoChris]

I use a flow meter on the hose for flushing the black tank. that way I can close the valve and let the water build up for a while without risk. as long as you know your and size you can fill it 1/2 to 3/4 of the way for a good final flush.

^--2x I do the same. I have a dedicated flow meter and hose (for black flush). I am surprised at how much "stuff" comes out on the first (and second and end of year third+) "clean water" dumps.

Chris

[Richter]

When I do the flush I go stand at my control panel to keep a check on the black tank level. Once it gets to 2/3 full I go open the valve. I figure if I'm standing at the panel monitoring the levels I won't get distracted by a squirrel and forget the task at hand.

You may want to keep in mind that there have been numerous complaints about the gauges not being accurate. In some cases, they have been for a while, then something sticks to a sensor, and they are no longer accurate. I, like many have mentioned, have found it better to measure the water input with a flow meter. I also try to not put more than a half-tank of flush water in, although I do it three times, normally. I’ve found that this, along with the Geo method when moving, helps to keep things pretty clean.

[Malco1]

I've never used a pressure regulator on the black tank rinse.

Rob

Me neither, you will never build up pressure because the line is open. There are no moving parts in the tank flush . If you must use a regulator, make sure you have a separate regulator just for that purpose.