Confused by black tank flush

[david-steph2018]

@NYSUPstater , your process (first paragraph) sounds essentially the same as I am proposing. Thanks.

@david-steph2018 , thanks for your unreliable camp water insight. DARN, I wish there was a fast path from the fresh water tank to the black tank. Maybe I should carry a hose that fits the [to be replaced] bathroom faucet. Then, we could accomplish nearly the same thing by towing with 2/3 fresh water, and transfer 1/3 to black water tank only on #2 demand, not #1.

I still don't understand the burp. If I experience it, I'll recognize it. But I'm seeking a mechanical understanding in advance. Perhaps... is the top of the tank often not level, or else above the top of the entrance elbow, if one exists? Then as more water goes in, it might displace trapped air? The point for me is that it seems like it MIGHT be that only SOME systems do this, and not all. That would make it a less reliable indicator.

There is a vent pipe from your black tank to the outside, generally up thru/out on the roof. Jump up there and double check. Once the water in the black tank is above the bottom of the vent pipe, there is no place for the displaced air to go except out the toilet when you flush. Just try not to look at the level indicator, at least once, and you will determine the time to dump the black tank when you get the "burp" when you flush.

 

[Dr.Lightning]

Ah ha... but... my toilet flush is only several ounces that happens at the time the foot pedal is pressed. There's no toilet tank for a sudden flow of volume water. No I haven't measured that volume, LOL. It's more like a "spritz" each time the foot pedal is pressed.

Note I *have* been thinking about installing a "shower toilet" like I have in the primary residence. ("Shower Toilet" is the anglicized Japanese term for a bidet, but is slightly different from a bidet. I'm not talking about an RV toilet inside an RV shower.) If I do add this, I may or may not upgrade to a tank toilet, as I've seen in some photos.

 

[rwdennis]

i have a water guage that screws on to the garden hose that tells you how many gallons were put in , so when i flush the black tank i fill it most of the way up (45 gallons) then dump , fill and repeat a few time till water comes out clear , got the guage from amazon , about 12 bucks , also use it to fill the water tank , so i know how much is put in .