Gravity Drains not Draining

[grakin]

I recently camped in Colorado (-5F!) at a full service campground.

I thought, "Hmmm...since I have water and sewer, I'll fill the inside tank, and use it when I want to shower, and then run outside and open all the low point drains and drain valve for the shower when I finish. I should be able to use the toilet normally, so that's cool."

I discovered some flaws in my thinking.

1st: In my TM, it seems like gravity draining (with open faucets and head removed) does not help the inside shower. Something froze in the lines going to the shower, and it was frozen when I started camping (I leave the low point drains and faucets/showers "open" all the time when I don't have water, so they had literally been open for a month or more). I was able to thaw it, but it quickly froze again after I drained the low points.

2nd: I didn't consider that the drain valves would freeze. They can and do. This was a minor annoyance with the gray water, but a big deal with the toilet. I didn't think with the toilet, and pulled the inside valve before trying the outside one. Fortunately it warmed up before things could freeze in that pipe. I had dumped some pink stuff down all the drains and the toilets to keep this from happening, but clearly I didn't dump enough, and I didn't consider that the ice would form on the *outlet* of the dump valves.

3rd: I assumed everything had traps in the gray water system, so there would be no oders if I left the gray water valve open while connected to sewer. That was VERY wrong. Don't do that, learn from my mistake! I thought I could leave the valve open and worry less about it freezing closed.

When it is warmer, I'm going to look at the pipe under the trailer and going to the shower. My suspicion is that it runs horizontal at some point, or maybe slightly "uphill" to the low point drains. I know that the water pipes under the sink do that and won't drain in my unit from the low points (I have to fix that!). I'm also going to seriously consider the heated valves, drain pipe (just for the gray water, don't think I need it for the black water pipe if I have a heated valve), and heat pad on the gray water tank. But I've got to think about how often I camp in these temperatures with hookups (it would be impractical to do this without hookups) and how inconvenient it is *really* to not use the campground facilities when available.

I think my toilet problems could have been solved easily - if I started with the toilet valve open, but the gray closed, and didn't use the gray tank, I think I could have easily managed dumping and such of that tank, so I learned an important lesson there. :)

On the other hand, the heater works great in the TM - I had a problem with not being able to completely drain the propane tanks due to the cold, but I was nice and toasty inside.

[Scott O]

Generally, you never want to open either your gray or black water valves until you are ready to dump. The pressure of a full tank helps them empty. Dump the toilet first, then the gray water to flush the hose. I don't know if this will help the freezing problem (maybe others can comment on this), but it is good general practice all the time.

[grakin]

Agreed on the dumping when tanks are full, black first then gray. The reason I left them open is they certainly would have frozen solid by the time I was able to fill the tanks, and thought I could "cheat". :/

[P and B]

Don't all drains that potentially connect to an open sewer have to have traps by code? If this is true, there shouldn't be any issue with leaving the gray valve open while you're hooked up. Don't think there's any reason to leave the black tank open all the time because it doesn't fill up as fast. What I usually do when I'm plugged in is leave the gray open. The night before we leave, I close it and let the gray tank fill up. The next morning I dump the black and then the gray as described above. With the TM, I also empty most of the Fresh water into the gray tank so I don't travel with the extra weight.

Phil

[Bill]

Interesting question, Phil. I just took a crawl under my TM to check it out. There are no household-style water traps (P-traps or U-traps) in either the gray water or black water dump lines. And the outlet from the toilet comes straight down from the toilet to the external dump valve - no water trap.

I'm not familiar with code for RVs, so I won't try to quote it. These are my own thoughts on the topic.

The trap function (preventing sewer gasses from rising into the living spaces) doesn't have to be performed by a water trap. In the case of the toilet, I suspect that the slide valve built into the bottom of the toilet serves the trap function. The seal, being waterproof, is really quite tight.

In the case of the gray water, I seem to recall that there are traps upstream from the holding tank. In other words, there is a water trap under the kitchen sink, and one under the bathroom sink. I just don't know about the tub, and I can't see up there. But since the sinks have water traps, it makes sense that the tub has one as well - otherwise there would be no point in installing the others.

By the way, there is another reason not to leave the slide valve under the toilet open. Go to the TM Reference Library, read the tutuorial on the toilet, and look for the phrase "black cone".

Bill

[mtnguy]

In the case of our TMs, I wonder if you quickly drain the gray water tank, if that would "pull" the water out of 1 or more traps, letting the residual water smell back through that point. I don't think the TM has a vented plumbing system like in our homes, and wondering if that is possible.

Just thinkn' out loud. :rolleyes:

Chap

[Bill]

Good question, Chap. As the water level in the gray tank drops, it would certainly create suction ("negative pressure") inside the tank if allowed to do so.

I rummaged around the RVIA web site (these are the folks that set standards for RVs), and under Adopted Standards, I found the following.

"Fixtures with traps and vents must be provided to protect against siphonage and back pressure."

and

"Vents to release gases from any waste holding tank must be provided."

I don't know if RVIA standards have the force of law, but since TMs display the RVIA sticker, they meet RVIA standards.

Bill

[rtcassel]

In the case of the gray water, I seem to recall that there are traps upstream from the holding tank. In other words, there is a water trap under the kitchen sink, and one under the bathroom sink. I just don't know about the tub, and I can't see up there. But since the sinks have water traps, it makes sense that the tub has one as well - otherwise there would be no point in installing the others.
On my TM, it looks like the water trap for the tub is inside the black box (with a circular screen) that hangs from the bottom of the TM below the tub. There are water lines and at least one wire that run through this box also. I think that there is a channel (through the styrofoam) from this box to the bathroom exhaust fan.

[rtcassel]

"Vents to release gases from any waste holding tank must be provided."

I don't know if RVIA standards have the force of law, but since TMs display the RVIA sticker, they meet RVIA standards.
In the summer when the gray water has been "percolating" for a few days, I can sometimes smell it on the bathroom side of the TM. Perhaps the GW tank is vented through a styrofoam channel and out the black box mentioned in the post above.

However, I have read on the web that the GW tank should be vented at its highest point, and this black box is near its lowest point. The highest part of the tank is on the door side. On my TM, there is space between the tank and the floor of the TM on the door side. Perhaps the tank is vented into this space?

[mjlaupp]

Actually there is a grey water vent installed on the TM. It's on the street side between the kitchen sink and the bathroom sink. My 2720SL has one P-trap below the kitchen sink that serves both the kitchen and bath sinks. The vent is connected here. I assume there is another P-trap under the bathtub. The sink vent serves as the vent for this P-trap as well.
Mike

[P and B]

I didn't think a simple "seal" would do for gas. That's why traps work so nicely- at least for relatively low pressure. I'm sure there are super sophisticated gas seals that don't involve water at the blocking medium but this is the RV business. I was always amazed at just how much "household" stuff they use. I can just imagine what the first RVs looked like!

BTW, I'd go look at my TM but it's under the tarp and it's snowing....