Can a waste tank overflow? And then what happens?

[Fairfieldwiz]

Long story short... There appears to be waste water on the ground near where my coach is stored. It appears to have been there for just a few days. I say "appears" because there is no sign of leakage from beneath. Gate valves are closed and dry. Nothing drippingv that I could see from anywhere.

My question: one of the gray water tanks is showing as 2/3 full on the stupid little light gauge. Could the tank actually be full and overflowing? My understanding is that an overflowing tank would back up inside the MH, right, not in the ground, right?

Opinions?

[fla tom]

With normal plumbing it would back up inside. With some (heposeal I believe is the name) over flow could occur on the roof (vents)

[old golfer guy]

When we first bought our RV I wanted to clean the black tank. So I hooked up the hose to fill it and then walked away to have a beer. DW came yelling from the MH saying that its flooding inside!!! The water was coming out of the toilet and spilling all over!!! You can rinse it out but keep an eye on things.

[bobmac]

Originally Posted by old golfer guy

When we first bought our RV I wanted to clean the black tank. So I hooked up the hose to fill it and then walked away to have a beer. DW came yelling from the MH saying that its flooding inside!!! The water was coming out of the toilet and spilling all over!!! You can rinse it out but keep an eye on things.

You are not the only new RV'er who has had such an initiation. Willing to bet you will never do it again!

[Old Scout]

...usually not--black tank, you see the level rise up and thru your toilet....gray tank--your shower floor is often the low point for gray water so you usually see it there first. Depending on how well they did it or the technique the manufacturer used to seal the drain lines to the tanks, there could be a possibility of some leaks at the tank[s] connections......

[96 Wideglide]

Like Old Scout said, black tank will come up the toilet, grey tank in the shower.
This is if you have properly working plumbing systems.

[FatChance]

If the seal in the toilet is good (water doesn't leak out of the bowl just sitting there) why wouldn't the black tank overflow just go up the vent to the roof (assuming you don't flush the toilet)?

Edit: We have a Thetford Aria Deluxe 2, other toilets could function differently, I suppose.

[hohenwald48]

Originally Posted by FatChance

If the seal in the toilet is good (water doesn't leak out of the bowl just sitting there) why wouldn't the black tank overflow just go up the vent to the roof (assuming you don't flush the toilet)?

Edit: We have a Thetford Aria Deluxe 2, other toilets could function differently, I suppose.

Because water can't run up hill. Or in this case, up pipe. Unless you apply pressure from some source such as a hose connected to a black tank rinser. Toilet seals aren't designed to withstand any pressure over a few inches of water column.

In normal operation (which I assume is what the OP is asking about) there is no source of pressure (other than gravity) in the black or gray tank.

[96 Wideglide]

Originally Posted by FatChance

If the seal in the toilet is good (water doesn't leak out of the bowl just sitting there) why wouldn't the black tank overflow just go up the vent to the roof (assuming you don't flush the toilet)?

Edit: We have a Thetford Aria Deluxe 2, other toilets could function differently, I suppose.

Your correct. It will.
The one time I tested this theory, I had the black tank flush on, with the drain valve closed. Let it go a little too long and flushed the toilet . It was pressurized . I'm sure a few more seconds it would have been comeing out on the roof.

[TechWriter]

Originally Posted by FatChance

If the seal in the toilet is good (water doesn't leak out of the bowl just sitting there) why wouldn't the black tank overflow just go up the vent to the roof (assuming you don't flush the toilet)?

Edit: We have a Thetford Aria Deluxe 2, other toilets could function differently, I suppose.

Yeah, I've done this a couple of times. Flushed my black tank using the built-in rinser, left it on too long, and right out the black tank stack.

Embarrassing and stinky!

[Old Scout]

….in "theory," the only way to "flood" the black tank is with the rinse/flush system.... the toilet is the high point for filling black tank [gravity wise]….you will see the toilet pipe fill first ….if you "pressurize" the tank, the vent pipe will eventually fill and over flow...base on what others have reported they have had happen INSIDE their coaches; regardless of design, I don't think I wouldn't trust the toilet seal to hold back the "flood"......

[EdInArk]

We have a friend who is a single lady that pulls a TT, and on one of our campouts a gentleman volunteered to help her hook up and, unbeknownst to her, he screwed the fresh water to the black tank flush and turned it on. A while later, she had a geyser on her roof. I was amazed when she told us nothing had overflowed inside. I've also heard of them flooding inside, but in at least one instance the toilet held.

As a side note, she won't let anyone help her now. I've walked over and said "Can I help?", and she curtly replies "I got it!"

[FatChance]

I was referring to the OP's question, "Can a waste tank overflow?" and both tanks can overflow in more than one way, I was just mentioning a second way the black tank can overflow.

As long as the black tank vent is open, the black tank cannot "pressurize". But, if something in the black tank clogs the vent while the tank rinse is flowing, it will pressurize with very unpleasant results that can be worse than just draining off the roof...

[All_talk]

Some RVs (like mine) have the bathroom sink run into the black tank, so if you had a good seal at the toilet your black flush should overflow the sink before venting out the roof.

I don't have a black flush fitting so have never tested the theory.

Gary