Black water tank fills with no usage

[Comm1]

Greetings!
We are full time for the past two months, and we have a strange issue.
2019 Coachmen Mirada 35LS, bath and a half. We made the decision to use the half bath as the primary for "black water usage" as we do not have a direct way to empty the holding tanks except by using a tote. We do not use the full bath toilet unless it is an extreme emergency.
The issue is the black tank for the full bath keeps filling up! The water level in the toilet does not go down. The gray water from the full bath is routed into the gray tank as it should. However, the last time we dumped the full bath black tank, there appeared to be "red" coloring from the deodorizing treatment used in the gray water tank.
Any ideas? HELP!!!

[aceinspp]

Most likely the two black tanks maybe connected together. Do you have two black tank vavles to drain either or?. Later JD

[doc73]

I agree I would look to see if maybe it's somehow piped in with a valve to the gray tank and maybe that valve is stuck open, in the case of a cable valve let's say or an electric valve. The next thing would be making sure that something isn't actually draining into that tank. More often than not I seem to read on here where showers or sinks or kitchens are actually routed into a black tank instead of a great tank. They seem to do whatever they want in these trailers / motorhomes.

[PopFla]

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

[bubbles]

Originally Posted by PopFla

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

So, is this the way your GT is plumbed?

[Gmoney67]

Originally Posted by PopFla

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

Don't think this is true my unit doesn't and my other 3 units didn't work that way.

[Mr. Dan]

Originally Posted by PopFla

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

Are you sure they almost always do? My bathroom sink drains into my bathroom gray tank in my current Wildcat and my previous 3 travel trailers.

[PopFla]

Originally Posted by bubbles

So, is this the way your GT is plumbed?

Originally Posted by Gmoney67

Don't think this is true my unit doesn't and my other 3 units didn't work that way.

Originally Posted by Mr. Dan

Are you sure they almost always do? My bathroom sink drains into my bathroom gray tank in my current Wildcat and my previous 3 travel trailers.

I haven't had it long enough to determine, but my last two MHs - A Coachman and a Thor - definitely did. Verified by running red dye down the sink drain and seeing which tank it drained from. Undyed water from the shower came out the grey tank, red water from the black tank. I have not owned a rig with more than one grey and one black tank.

[Comanchecreek]

Originally Posted by PopFla

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

I've never seen that kind of a setup, not that it's not plumbed that way by someone, just all of my sinks have always gone into the bathroom grey water tank. Some of my earlier rigs shared a bathroom grey water, and a kitchen grey water, but all had toilet only black water tanks.

When you are on pump only does the pump run periodically? That would be a sign that you have a slight leak in your toilet. It doesn't take much of a leak to add up to a fair amount of water over time. Just something else to check.

[bubbles]

Originally Posted by PopFla

I haven't had it long enough to determine, but my last two MHs - A Coachman and a Thor - definitely did. Verified by running red dye down the sink drain and seeing which tank it drained from. Undyed water from the shower came out the grey tank, red water from the black tank. I have not owned a rig with more than one grey and one black tank.

I agree with your statement about some units plumbed gray to black holding (there have been posts referencing this) but not the majority and not because of your reasoning. Your unit is a single lav and gray water is to gray holding and black water (toilet) is to black holding.

[NMWildcat]

The OP just needs to empty the tanks and then run one fixture at a time to determine what tank is filling if there is question about it. Then they will know if they need to adjust how they use the plumbing. It always amazes me how little some folks know about their own RV.

[5picker]

Motorhomes/diesel pushers are sometimes plumbed with the the bathroom sink running to the black tank. They can often fit much larger black & grey tanks in those units so to 'fill' the black tank at a comparable fill rate as the grey, they'll run the bathroom sink into the black tank.

Most travel trailers and 5th wheels are different but some larger 5th wheels can have a sink and the washer go to the black tank. Every rig is different. Like Scott, I'm always amazed how little some folks know about THEIR R/V and how some folks believe EVERY R/V is exactly like theirs.

[DrLewie]

My long-gone '08 Cardinal definitely drained the bathroom sink into the black tank. I found out the hard way,

[Reverse_snowbird]

Originally Posted by NMWildcat

The OP just needs to empty the tanks and then run one fixture at a time to determine what tank is filling if there is question about it. Then they will know if they need to adjust how they use the plumbing.

That would be my recommendation.
Our REV bathroom sink drains into the black tank. With the macerator toilet, using the bathroom sink makes rinsing the black tank easier, but we have to watch how much we water we use in the bathroom sink. Washing hands in the kitchen sink is now the way we keep from filling up the black tank.

[Comm1]

Thanks everyone, gives me a different perspective on things. We purchased this rig in January, traded in our 2012 Coachmen 32DS Class A, but it only had a single bath.

My original thought was the water supply for the toilet, which comes in before the ball valve, was leaking without us knowing. We had both toilets changed when we purchased this rig to elongated bowl toilets. I never would have thought of the sink running into the black tank, but in a way it makes sense. We'll have to try a "dye water" test and see if it that is all it is.

Unfortunately, I cannot get to my tanks as I'm recovering from back surgery I had in May, it will be a few more months before I can contort into position to look at them.

Again, thanks for your ideas and making me feel I'm not really going as crazy as you would think!!!

[Comm1]

Sorry, forgot to answer the questions...

We have two black tanks, one in the wet bay and one on it's own at the back where the "master bathroom" is. They each have their own drain and flush system. Since we have only been using the rig for "camping" up until now, we have never used the water pump other than for bathroom breaks while traveling as we have always stayed at campgrounds with either full hook up or at minimum water and electric.

We dumped the tank on Tuesday, and today we are reading at 1/3. If it is filling from the sink, that would be about right.

We have owned two travel trailers and two motor homes prior to this, but this is our first with more than one bath. After all these years of camping, there is always something to learn!!! LOL!!

[CedarCreekWoody]

You really dont have to use dye. Empty all of your tanks, close all valves. Run a couple gallons of water into the bathroom sink. Open the valves one at a time. Which one drained a gallon or two? You can do this for each sink you are unsure of, and you can do it home if you've completely drained all tanks at the campground dump.

[JohnMirada]

We had a 2015 Mirada 35LS and it had two Black tanks. The "master bath" sink did drain into the rear black tank. We found that out when we thought the bathroom sink was plugged but on a whim I checked the black tank level and it was full. After dumping the black water tank the sink drained just fine. Nothing wrong with your unit - that's just the way it's plumbed.

[doanshop]

Originally Posted by PopFla

Bathroom sinks almost always drain to the black tank. That's done intentionally to add water into that tank to keep....stuff.....in the black tank from drying out and forming clogs in the tank. It helps keep everything well liquified to facilitate emptying the tank.

Something I didn't know or think about never had a problem with black tank filling up fast but I will have to test my tanks now to see if bathroom sink is plumbed to black tank thanks for info . I did add a grey tank for longer boon docking .Now I'm curious about it sink and black tank . Again thanks for info .

[Dirt Sifter]

Glad the OP got the info he needed. I am often impressed by how old RVer's forget how little they knew about RVing when they first started or changed rigs. So fortunate to have those who strive to make positive contributions to help solve issues.