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InterBlog · 07-14-2018, 05:21 AM

We have three recently-active toilet threads on this subforum, but this is a different topic altogether: the issue of proper tank venting.

Our model of Airstream Interstate has separate gray and black tanks. The black tank is internal under the street side cabinetry. The gray tank is external, slung under the chassis, more-or-less underneath the black tank.

In an interesting twist of engineering, both tanks were plumbed to the same roof vent line using a Y connector.

We replaced our original nighmarish Thetford toilet with a Dometic late last year after developing major odor problems. You can read about that adventure on this blog post here and this Air Forums thread here.

The replacement job did result in an improvement, but there is still some detectable odor. Dollars to donuts, that has something to do with improper air flow through the whole plumbing system. In other words, we only solved half the issue when we upgraded the potty.

Which brings me round to our rig's nightmarish tank vent installation. You can see that in the image below. For the moment as a stop-gap, I've got that gruesome hack job sealed up with a Fort Knox-style re-caulk application (Sikaflex 221), but it's on my late-2018 DIY cool-weather project list to open up what is sure to be revealed as a major can of worms and replace it with something better.

What is that something better? Has anyone installed a 360 Siphon roof vent on their Interstate? If so, what feedback do you have? Is it worth the trouble and does it do what it claims to do? Or should I be considering other vent products?

Thanks.

Tincampers · 07-14-2018, 05:35 AM

I wonder if a solar powered fan equipped vent would be a better alternative?

https://amzn.to/2zFOxAW

InterBlog · 07-14-2018, 05:41 AM

Quote:

Originally Posted by Tincampers

I wonder if a solar powered fan equipped vent would be a better alternative?

The thought crossed my mind. Nobody could live with a "composting" (air quotes) toilet if it were not under active negative pressure all the time. So why not conventional RV toilets too?

Either solar powered or something that could be wired in to operate electively on a switch, like our electrical control panel fan has been done.

To some of the others who are reading this, yes, we do have a roof fan in the wet bath, but that's actually part of the problem, not part of the solution. If the holding tanks are not venting properly, then the main wet bath exhaust fan is only going to make the pass-through issue worse.

TheGreatleys · 07-14-2018, 06:18 AM

Quote:

Originally Posted by InterBlog

The thought crossed my mind. Nobody could live with a "composting" (air quotes) toilet if it were not under active negative pressure all the time. So why not conventional RV toilets too?

Either solar powered or something that could be wired in to operate electively on a switch, like our electrical control panel fan has been done.

To some of the others who are reading this, yes, we do have a roof fan in the wet bath, but that's actually part of the problem, not part of the solution. If the holding tanks are not venting properly, then the main wet bath exhaust fan is only going to make the pass-through issue worse.

FWIW, lots of people live with composting toilets without vents. The single bucket method is far older and more prevalent than the $1000 package models. You have to use a LOT of cover material, but even mixed solids and liquids don't smell if properly managed. The package composting toilets with urine diversion, an auger, and a fan, are mostly geared toward minimizing maintenance frequency.

I do agree that a fan for a regular RV toilet would be worthwhile. I'd try to find a way to build it into the toilet itself, under the seat. One of my favorite features of my composting toilet is that the exhaust fan captures bathroom odors eminating, not just from the toilet, but from its occupant. No matter what I'm doing in there, my wife sitting just outside the door can't smell a thing.

I wonder if a replacement toilet seat could be manufactured with a few holes in the back by the hinge to pull air into an exhaust fan.

GMFL · 07-14-2018, 06:59 AM

Sewer gases are very corrosive I’m not sure that little fan motor would last very long in those gases unless it is sealed better than I think it is.
Just a thought.

InterBlog · 07-14-2018, 07:47 AM

Quote:

Originally Posted by GMFL

Sewer gases are very corrosive I’m not sure that little fan motor would last very long in those gases unless it is sealed better than I think it is.
Just a thought.

Yes, I saw those reviews. The idea is sound, but the execution is poor - just like so many other components on our rigs. Cheap imported stuff.

The odds of my husband engineering a stainless steel variant on the fan theme are high, I think. Either that or we verify that a Bernoulli-style device really would work.

InterBlog · 07-14-2018, 09:03 AM

I just found this option on ModMyRV. I haven't looked at that site in years.

http://www.modmyrv.com/2008/10/02/rv...dor-controller

gmillerok1 · 07-14-2018, 09:11 AM

Quote:

Originally Posted by InterBlog

I just found this option on ModMyRV. I haven't looked at that site in years.

http://www.modmyrv.com/2008/10/02/rv...dor-controller

Not sure that's such a good idea.

https://www.bbb.org/central-texas/bu...and-complaints

Plus, the former web site is no longer functioning.

gmillerok1 · 07-14-2018, 10:06 AM

Here' a do it yourself version:

http://roadtreklife.blogspot.com/201...tank-vent.html

InterBlog · 07-14-2018, 10:14 AM

Yes, to my despair, I looked more deeply into the Lil Stank only to find that it is no longer for sale. Manufacturer appears to be tango uniform.

But the Roadtrek Life option looks promising. Thanks for that.

LB_3 · 07-14-2018, 11:29 AM

Since there is only one vent line, these devices only real function is to create a negative pressure on the tank to prevent gassed entering the cab when you flush. Probably worth while but no need for continuous operation unless a second vent is added.

Jim Flower · 07-14-2018, 01:37 PM

I use a Camco Cyclone Vent on both the black and grey tank vents on my Airstream. I like them because they work and there are no parts that wear out. Trouble and odour free for the past six years.
https://images-na.ssl-images-amazon....NL._SY450_.jpg

guskmg · 07-14-2018, 01:57 PM

I have use both Cyclone and a 360. They both work good and the 360 is a much lower profile if you later add a solor panel over it. BTW, that did not make any difference in the performance.
guskmg

InterBlog · 07-14-2018, 01:57 PM

Quote:

Originally Posted by LB_3

Since there is only one vent line, these devices only real function is to create a negative pressure on the tank to prevent gassed entering the cab when you flush. Probably worth while but no need for continuous operation unless a second vent is added.

That assumes that the toilet is air tight, which we are well aware is not true. Not the Thetford and not the Dometic (although the Dometic is better).

A W Warn · 07-14-2018, 02:03 PM

my $0.02:
I ask myself, why does a black or gray holding tank need to be vented?
The ONLY two reason I can think of are:
(a) to let air in or out as waste flows so that a vacuum is not created within the plumbing (pulling water out of traps)
(b) to let methane, and other gases, escape when created by organisms in the sewerage.

Since both the black and gray tanks are holding tanks that are frequently emptied, air exchange is not necessary for the health of the system. And, mechanically exchanging that air/gas inside the tanks with a fan could cause odor to be notice outside and maybe inside the trailer.

IMO, the simplest/cheapest vent that will keep rain from leaking in around the vent is adequate. Adding a screen to keep bugs/flies/animals out is a good idea. Adding vents that have moving parts is a not necessary and adds another level of maintenance.

I replaced my vents a few times over the years, and used the same vents as were originally installed.

A W Warn · 07-14-2018, 02:12 PM

Quote:

Originally Posted by LB_3

Since there is only one vent line, these devices only real function is to create a negative pressure on the tank to prevent gassed entering the cab when you flush. Probably worth while but no need for continuous operation unless a second vent is added.

A sewer vent does not create any pressure, it is just an opening to atmosphere.

A vent fan (toilet exhaust, Fantastic, etc) can create negative pressure that will draw air/toilet gas into the living space through the sewer vent and then through an open toilet flapper valve or leaking toilet flange gasket.

The sewer vent system in our Airstream is a combination of air admittance valves (lets air in) and vents (lets air out) to atmosphere. Air in the tank is pushed out of the tank through the vent as the tank fills with waste/water. The water/waste flowing through pipes can/does create both negative pressure and positive pressure. This pressure is relieved by the sewer vent system.

add edit:
If a device is added to a sewer vent that pulls air out of the tanks, the air admittance valves on the interior the trailer will let air into the sewer drain pipes creating a negative pressure inside the living space. Replacement air will come inside through any crack and crevice. This air exchange will affect the cooling and heating of the interior space during temperature extremes.

Boxster1971 · 07-14-2018, 02:19 PM

IB - you are getting a lot of replies to your question that are mostly noise. FYI - Airstream used the 360 Siphon vent on my Interstate. I think they are standard vents used by Airstream since about 2010. The 360 Siphon is a good quality tank vent that has worked well for me in last six years.

fran&frank · 07-14-2018, 02:47 PM

I agree wit the last post. With a standard toilet and black tank you don't need a fan to vent the system. You have traps on your drains and a valve on your toilet to prevent sewer gas from getting into the living space. The vent is to prevent pressure from building up so water and waste flow down the drains with no resistance, that's it. The 360 siphon vents work well on my trailer.-- Frank

alantbird · 07-14-2018, 05:04 PM

Quote:

Originally Posted by Jim Flower

I use a Camco Cyclone Vent on both the black and grey tank vents on my Airstream. I like them because they work and there are no parts that wear out. Trouble and odour free for the past six years.
https://images-na.ssl-images-amazon....NL._SY450_.jpg

Solved our problem instantly

InterBlog · 07-14-2018, 05:13 PM

The decision tree on this one boils down to the following:

Does it stink, or does it NOT stink?

In our case, it stinks, even after toilet replacement and even after we concluded that our black tank is not the problem (it is water tight).

The available toilets to fit our rig configuration are not air tight - none of them. The choices each amount to cheap crap made in China or some such place. I can't fit a marine-quality toilet in there. That was the subject of a previous thread I linked to in #1.

Ergo, I need a better vent, possibly active instead of passive. Roadtrek Life, one of the most esteemed Class B DIYers on the internet, concluded similarly and made his own active venting system. I may try the Siphon 360 and if that fails to rectify the situation, then I may go active instead.