Black Water Flush Metrics

[howson]

Based on the long thread started by KirbyRVA and the recent work I did to move my black tank flush, I thought I'd try to figure out a baseline for my system and (hopefully) get a few more to compare (from all of you).

The testing methodology is far from "scientific", but I think with enough information we can draw some general conclusions.

What I did was hook up a 50' hose to my house and then to the black water inlet. The black tank was empty, and knife and add-on Valterra valve were both open (and left open). No drain hose as I knew the tank was clean.

The pressure gauge showed ~50 psi at the black water flush inlet (no regulator in the line). Note the hose is connected to my home's system at a spot quite distant from the actual house as the spigot was added to a shed for the camper. (Easily 100' of pex running underground from the house to the shed.)



I then turned on the water for a minute (with the volume meter recording the flow). Pressure dropped during the test to ~20 psi.



I ran the test three times. The results on the volume meter were 2.4, 2.5 and 2.5 gallons in the 1 minute time period.



So there you have it. How about yours?

[Cate&Rob]

howson
Hi Howard,

I did not measure my system exactly the same way, but measured as you have done . . . my results would be almost identical. Static pressure of 50 psi and flow pressure of <20 psi are the same. To the point discussed in the other threads . . . Folks “think” they are flushing the tank at 50 psi when the working pressure is less than half that.

Rob

[motocamper]

I'll just say that pic of the black flush running out on the driveway is an example of a man supremely confident in his last flush job

[boyscout]

I'll just say that pic of the black flush running out on the driveway is an example of a man supremely confident in his last flush job

I was figuring howson doesn't consume anything but water. What a saint!

I have one of those meters but have never done the test. I'm surprised at the small amount of water reported.

I dump black while flushing, then when the trickle is clear I close the dump valve and let black tank flush re-fill the tank. For six minutes. Don't know how I arrived at that but it seemed safe, and it also seemed effective because when I pull the dump valve again I get a REALLY good gush out of the black tank and it's never clean, it always brings out more stuff.

According to Howard's test I'm only putting in about 15 gallons, surprising. I would have guessed based on what comes out closer 20 to 25 gallons. Now I'll have to get scientific about it!

Thanks as always for your work Howard.

[Cate&Rob]

I'll just say that pic of the black flush running out on the driveway is an example of a man supremely confident in his last flush job

LOL! I thought the same thing . . . I've never been confident enough to do that. Maybe into a pail and what looks like clear water still has little bits.

Rob

[Second Chance]

Based on the long thread started by KirbyRVA and the recent work I did to move my black tank flush, I thought I'd try to figure out a baseline for my system and (hopefully) get a few more to compare (from all of you).

The testing methodology is far from "scientific", but I think with enough information we can draw some general conclusions.

What I did was hook up a 50' hose to my house and then to the black water inlet. The black tank was empty, and knife and add-on Valterra valve were both open (and left open). No drain hose as I knew the tank was clean.

The pressure gauge showed ~50 psi at the black water flush inlet (no regulator in the line). Note the hose is connected to my home's system at a spot quite distant from the actual house as the spigot was added to a shed for the camper. (Easily 100' of pex running underground from the house to the shed.)

I then turned on the water for a minute (with the volume meter recording the flow). Pressure dropped during the test to ~20 psi.

I ran the test three times. The results on the volume meter were 2.4, 2.5 and 2.5 gallons in the 1 minute time period.

So there you have it. How about yours?

I was excited when I heard about this particular water meter... and then I started reading the reviews on Amazon. The ratings are pretty low and are almost totally related to breakage of the flange at the body. Have you had any issues with yours?

Rob

[howson]

I was excited when I heard about this particular water meter... and then I started reading the reviews on Amazon. The ratings are pretty low and are almost totally related to breakage of the flange at the body. Have you had any issues with yours?

Rob

None. But...they are not robust units so I have low expectations for how long they will last.

I have two of them, one I use to monitor fresh water usage and the other for the black tank flush.

To those that will ask the inevitable "why" question...I travel with 5 gallons of water in the fresh tank so the volume meter allows me to put in exactly that amount each time. No extra water weight while towing. The black tank flush meter allows me to know how much water has flushed through the black tank. Nothing cosmic about that one other than my curiosity.