Why does the water back wash into the tub?

[stowaways]

Not sure if the terminology is right, but here's the idea. We don't have a gray tank in our '69 Sovereign, so we keep a small red hose attached and slowly let the gray drain away (only when and where permissible, of course).

When we use the bath sink, it drains fine. When we use the shower drain, eventually it drains okay. But if there's any water in the tub whatsoever, and you use any other sink, the water backs up into the tub. Shouldn't it all just drain out the drain out valve?

We've cleaned and flushed the water lines, hot water tank, plunged, etc.

Any ideas?

PS once we got over the boiled out battery crisis, we're actually enjoying the renovation again. All new screens last night! Yay! And the new blinds and cushions are on the way.

Thanks for the helpful tips and sharing in our fun!

[Inland RV Center, In]

Originally Posted by stowaways

Not sure if the terminology is right, but here's the idea. We don't have a gray tank in our '69 Sovereign, so we keep a small red hose attached and slowly let the gray drain away (only when and where permissible, of course).

When we use the bath sink, it drains fine. When we use the shower drain, eventually it drains okay. But if there's any water in the tub whatsoever, and you use any other sink, the water backs up into the tub. Shouldn't it all just drain out the drain out valve?

We've cleaned and flushed the water lines, hot water tank, plunged, etc.

Any ideas?

PS once we got over the boiled out battery crisis, we're actually enjoying the renovation again. All new screens last night! Yay! And the new blinds and cushions are on the way.

Thanks for the helpful tips and sharing in our fun!

The tub water drains to the same place as the sinks.

Be patient, and wait 15 minutes or so, since your using a small hose.

If your flushing away a lot of water, it will back up into the tub, since thats the lowest part of the system, but that will drain away also.

Andy

[SteveH]

This is only my idea, but it sounds like the water is not able to drain thru the "small red hose" fast enough.

I would try the same situation with a large sewer hose and see if it changes.

[Lumatic]

Check your roof vents

[Minno]

Funny thing water - it can make it's own decision and seek it's own level. I'm guessing that the red hose you're using to drain the gray water is small enough that water is backing up into the tub. When the tub drains, it will fill the drain line completely since the hose is the restriction. Then, when you add more water to the drain line (like from the bathroom sink), the water will go to the lowest place possible. In your case, the bathtub. And since the drain plumbing is already full of water, it will flow to the bathtub quite easily. So even though you're draiing the bathtub via the hose, the water from the higher sink will flow into the drain, and backup into the tub, because the hose is already full of water draining out. You have two 1 1/2" or 1 1/4" drains trying to go out a single 3/4" or 1/2" hose. The tub is acting like a gray water tank and holding the water until it can drain out of the hose.

Chris
Chris

[samb]

My guess is that it is the laws of physics rather than a problem in the trailer drains.
I would bet that the "small red hose" is the problem. It most likely is restricting the flow to a rate of less than the other drains, especially in combination. In that case, the water takes the path of least resistance ........ into the tub, the next lowest point.
To check this theory, remove the red hose and the cap it attaches to so you have a full 3" drain with no restrictions. I am guessing you have this option from the setup on my trailer. Then drain some sinks and shower in ways that previously cause problems and see if the problem is reduced or eliminated.
I, too, have no grey tank and use your same method. When I dump my kitchen sink through my "small black hose" it will sometimes back up in the tub. My cure is to slow the sink drain slightly so I have no backup. Hope this helps.
Sam

[Jim Foster]

I think you will find that the sinks flow into the drain between the tub and the final exit. If water is backed up into the tub, the exit drain is also full of water, so any water put down the sink drain will flow to the lowest point, which is the tub.

I once was hooked to our large "Blue Boy" with a small hose and had the shower water back up into the tub. The Blue Boy was empty, but I had not opened the drain cap, so air could not exit the Blue Boy as water entered. As soon as the air pressure in the Blue Boy built up, the water could no longer enter it and backed up. It doesn't take much to cause sink water to back up into the tub.

[purman]

Just make sure the black tank valve stays closed. You don't want any of that coming up in the tub....

[HowieE]

Sounds like you are building pressure in the gray water system. This could be because of the Small Drain hose and water is coming into the system faster than it can drain. As mentioned above try a full size drain hose or find a spot where you can just open the drain directly to the ground and try it there.

If you still have a problem depending where the vent is tied in flush the roof vent and try again.

[airstreamjudy]

Lumatic - tell us about the "roof vents". What's your theory?

[stowaways]

thanks all... we suspected the red hose. Will try experiment with slinkie and see if we get a different result! : )

[3 Dog Nite]

We've learned in previous posts that water seeks it own level. Is the end of the red hose lower than the tub? Does the red hose go over a small hill, then back down? This would create a drain trap which would cause more resistance in draining.

Ricky