couple of plumbing questions

[BG6]

If Methane is present it makes pressure so it is always flowing from the vent, even the slightest pressure will push it our a bottom vent. The pressure won't build up and suddenly push accumulated gas out the vent.

Not so.

Methane is the primary component of natural gas.  It doesn't "make pressure" any more than any other gas, or people wouldn't have to buy it.

[BG6]

Today's job is to start to re-plumb the coach,

To make the job less daunting, the vent doesn't have to be large, and can be made with flexible tubing.  All that matters is that it taps from the high point in the tank (or near enough to it) and that it vents past the roofline, and rises continuously.  That lets you route it where it's convenient.

[BG6]

Hey Ace, maybe if you ducted the vent into your engine air intake, all that methane would increase your HP?  LOL  Jack

Briefly.

It wouldn't take more than a few seconds for all of the methane to be carried into the engine.  After that, it would just be air.

[Len Silva]

In my old 4104, I used 1-1/2" swimming pool vacuum hose and routed it up behind the refrigerator and terminated at the top of the refer vent.  No extra hole in the roof.

[gus]

Since my drain/vent system is probably different than most I have "anti-siphon trap vent devices" (Love that name). I thought "check valve" sounded a bit simpler since that's what it is. My kitchen sink and wash basin are on dedicated drains with AAV's . The toilet and tub are on a different line from those. The main drain empties into the bottom of my waste tank so AAV's are necessary. They are necessary because I can hear them taking in air.  Wet vents would not work here because of the distances between fixtures. The PO assured me that the bus was plumbed by a licensed plumber and I had no reason to doubt him, even though it was done in a different code zone.

I said that the primary purpose of a building drain vent is to take air in, not vent methane because my plumbing manual says nothing about sewer gases in that section, all it discusses is taking fresh air in to prevent a vacumn in the system. Since I'm not a plumber I can only assume that gas is not a problem since there is no mention of it. I didn't bring up the subject of building vent systems, this was first introduced under the name of "fixed structures" which, I assumed, means buildings?

Loop vents are allowed by some codes so the accumulation of gas at the top of the loop doesn't seem to be a problem.

We started out discussing the explosive danger of methane but now seem to have changed to sewer gas and odors. Now I read that methane is not the primary concern??  Obviously nobody would vent sewer gas into a living space, otherwise why bother with traps?

I'm pretty sure I could smell sewer gas if it infiltrated the bus!! I'm also certain I can figure out what "secondary vent" means.

It is absolutely correct that methane is the primary gas produced by anaerobic bacteria reaction. It has been many years since I delved into chemistry and I got them reversed. Carbon dioxide is secondary to methane, not primary.

After a bit of research prodded by this discussion it now appears that my RV waste tank may not even have significant anaerobic activity because the waste is agitated so much and so much oxygen is introduced into the tank from the two AAV's, the toilet and the tank vent (when the tank is emptied). It seems anaerobic bacteria don't like agitation. Interesting thought!

I've read articles about sewer fires and explosions, but not ones originating in homes. The problem seems to be in the municipal system, not the home. And, again, never heard of an RV having a methane problem.

Since the building Code is divided into three zones and can be overriden by local codes it seems to me that the people writing these codes can't seem to agree on what is lawful or safe. This leaves me with the impression that in many cases there is more politics and special interest involved than science. I have to assume that the RV code isn't much better since it is based on the building codes.

"And, frankly, some of the counterarguments advanced have just been plain wrong", from a recent post, with no mention of codes, sounds like saying another poster is wrong to me? Forum posts more informative and less indignant would seem to be most beneficial to all.

I don't remember saying or reading any other post saying that we should ignore all rules and regulations and do as we please or that anyone should build anything they want? I do, however, remembering saying that we should think. I hadn't really thought of codes in terms of fascism or anarchy even though they are so rigid and often, to me, not clearly thought through. My house plumber fully agreed that PB is superior in all ways to Cu but said "the code" doesn't allow it. It would be wonderful if these codes could protect us from all but 0.001 % of danger.

My ole Grandpappy said to beware engineers, he didn't say eliminate or ignore them. I have a piece of paper that says I am an engineer, but I don't take it too seriously, and my son is a Boeing aerospace engineer, but he doesn't take his title too seriously either.

[sweeney153]

Gus
There is another point to consider.
On a structure there is an exit trap and in most jurisdictions an exit vent.  This effectively isolates the "air" in the house system from the sewer system. In an RV system the two are the same system.

My $.02

[gus]

Sweeney15,

Thanks. I wondered about that?

From your post I understand that the exit trap is on the main house line after all house lines and that the exit vent is also there?

I thought that any municipal sewer would have to be vented somehow and isolated from home sewer systems but I didn't know how it was done.

However, I don't understand how a septic tank is vented or isolated? Mine does not appear to have either a trap or a vent except for the drain vents?

It appears to me that fresh air is drawn into my RV system through the drain vents every time liquid flows through the drain lines, same as in a building. Also, as the tank fills it forces out any gas and when it is emptied it sucks in fresh air.

[sweeney153]

I have not done much with septic systems. You are correct that they do not have an exit trap. When I first moved out of the city and built my house I put in an exit trap and got dinged by the inspector. My understanding is that you don’t need or want an exit trap with a septic. You don’t have huge volumes of water rushing by your house main causing a venture effect sucking out you traps and the septic tank works with anaerobic bacteria, so they don’t like fresh air. Any build up of gases would be vented thru your main vent on the roof. That’s my understanding but as I said I never worked on septics except my own so if some one here has more knowledge and finds a mistake, Please fell free to correct me.

[gus]

Sweeney15,

Thanks, makes sense to me.

[niles500]

"the septic tank works with anaerobic bacteria, so they don’t like fresh air."

That is the definition of "anaerobic" - FWIW

[sweeney153]

Niles

I know that and I am glad you do too.

[kyle4501]

Just to be anal about the function of the bacteria in a septic tank system. . . 

Anaerobic bacteria perform the first treatment of the wastewater, generating gas that is vented through the vent stack of the building's plumbing, and breaking the solids into a liquid form.  The oxygen-free conditions inside the septic tank also deactivate some of the disease germs that are found in sewage.


The drainfield provides secondary treatment of the sewage by allowing aerobic (oxygen-using) bacteria to continue deactivating the disease germs that remain in the wastewater.


Surprising how much goes on in the black box after you flush. 

I'd like to stay outside of that box.   

[sweeney153]

Kyle

Excellent explanation.

 And I think is appropriate to be anal about septics

[gus]

Niles

Sweeney and I know that and are glad you do too!

Kyle,

This brings me to another question. If anaerobic bacteria change the solids to liquid why does the septic tank need to be pumped?

And, if it does, how often - roughly?

Years ago I opened the top of my septic tank. What I found surprised me. There was a pink colored 3", tough, almost like plastic, layer on top of the liquid.

What really surprised me was the liquid underneath had no odor whatsoever?? I expected it to really stink?

[kyle4501]

Obviously all the solids aren't reduced to liquid.
Frequency of pumping out the solids varies with how it's used & what is put in it.

I've known septic systems that have lasted 20 years with no maintenance, I've also known some that don't last 2.

On the one that lasted the longest, if they didn't eat it, it didn't go in the toilet . . . .

Garbage disposers aren't good.
Harsh chemicals aren't either.
Cigarette butts & certain feminine products won't break down.

 A google search can provide lots more stinking details for those who don't want to think outside the box.