Newbie here, Dumb question: How to know if black tank really is full?

[gDanColeman]

So, I'm a new Grand Design owner. I am camping now for my 3rd time. I have booked 10 nights boondocking (dump station is miles away). I have completed 9 nights so far -- no problems. This morning my black tank sensor on the panel is indicating full. Oh crap (pun intended), is that an emergency? Does that mean no more usage until I empty it? Is there no room to spare? I have no idea. Guess I'll have to pack up and leave earlier than planned. Replies to this thread will tell me what to do next time. Thanks to all who advise.

[TedS]

I know the tank is really full when the toilet burps when flushed.

[howson]

So, I'm a new Grand Design owner. I am camping now for my 3rd time. I have booked 10 nights boondocking (dump station is miles away). I have completed 9 nights so far -- no problems. This morning my black tank sensor on the panel is indicating full. Oh crap (pun intended), is that an emergency? Does that mean no more usage until I empty it? Is there no room to spare? I have no idea. Guess I'll have to pack up and leave earlier than planned. Replies to this thread will tell me what to do next time. Thanks to all who advise.

Typically a toilet, when flushed, will "burp" when it's nearly full. It's literally a sound you'll hear.

The black tank in your 15BH has a 37 gallon capacity. Based on the location where it's mounted, the toilet is mounted directly above the tank. This is good -- a straight shot from toilet to tank. So you could actually look down the toilet to see how close the tank contents are to the top of the tank. How to do this? Turn off the water supply to the trailer. Then flush the toilet and while holding it open peer down with a flashlight. (This is not a normal process, just an option if you're curious.)

What I do not recommend is relying on the lights on the panel as they are notoriously inaccurate. What happens is foreign material sticks to the sensors which results in erroneous readings. I haven't used the sensors in my rig for years -- I rely on a regular dump schedule based on number of days. Typically at a full hookup site the grays get dumped every other day. For the two of us, the black actually can go for many days before requiring a dump.

Finally, as I initially learned from Cate&Rob , after dumping the black tank add at least 5 gallons (some add up to 10!) of water to the tank (via the black tank flush). Most of us use a small water meter inline with the black tank flush hose (obviously with the black tank valve closed) to accurately measure how much is added. WARNING: DO NOT walk away while adding the water to the black tank. Some owners have burst their black tanks because they became distracted while adding water to the black tank.



I hope this helps.

Howard

Edit: You beat me to it, TedS

[Cate&Rob]

The level indicator lights are notorious for being incorrect. The black tank will back up the pipe from tank to toilet when the tank is absolutely full.

Rob

[Scott'n'Wendy]

Finally, as I initially learned from Cate&Rob , after dumping the black tank add at least 5 gallons (some add up to 10!) of water to the tank (via the black tank flush). Most of us use a small water meter inline with the black tank flush hose (obviously with the black tank valve closed) to accurately measure how much is added. WARNING: DO NOT walk away while adding the water to the black tank. Some owners have burst their black tanks because they became distracted while adding water to the black tank.

Those of us that don't bother with flow meters go by the bowl full after a dump. 3 bowls after dumping, Additional 1/2 bowl with each material dump.

[AlexPeterson]

The factory level sensors only indicate that you have 12v power - not much else.

[TucsonJim]

Here's a little more information on the "burp" some folks are talking about.

There are two holes cut into the top of the black tank. One hole is where the waste from the toilet enters the tank. The other hole is for a vent pipe that runs up to the roof.

As you flush the toilet, waste and water dump into the black tank due to gravity. This added waste displaces air in the tank which goes in two directions. Some of the air goes up the vent pipe, and some comes back into the RV. When the tank gets full enough that liquid reaches the level of the tank vent pipe, much more air comes back up through the toilet. This is the distinctive "burp" that is mentioned. If I see the burp, I know that I have about 12-15 more flushes before the liquid starts to collect at the base of the toilet and I'm completely full.

Jim

[SBARLAG]

I agree that tank sensors are notorious for being inaccurate. Grand Design's parent company, Winnebago, uses probes based off of a "sonar" application,,,no probes punchering the tank, which means no debris caught on a probe. Much more accurate.

[JBill9694]

Nothing to add with respect to your main question, gDanColeman, just wanted to throw out that you may be a candidate for an RV wastewater or sewer tote. No personal experience, but others here can provide a world of advice.

[ncitro]

The only thing I can add is if you are looking for accurate gauges I am really happy with the Seelevel monitoring system. I have had it for several years and have installed it on two friends rigs and it works great. Sensors stick to the outside of the tanks so no buildup of paper or "residue" issues. I initially got it for better reading of the black, but like most here find that gurgling tells the tale there. Where it really shines is for reading the fresh while boondocking. Knowing the difference that we are at 45% and not "between 1/3 and 2/3" makes a huge difference for us. Also when flushing my black tank it lets me watch the level rise (I have a second monitor in the Nautilus bay), and pull the lever when it gets up to 90%.

[TravelHabit]

My advice is to never let your tank get too full (a burp indicates it is too full). I found the seal to the toilet is not watertight so it is very likely that waste water will seep out when towing. See this thread black-tank-flange-seal-insufficient-solved for more information. After a few days I turn off the pump and just use a flashlight to quickly see the level (even though I now have a good seal).