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How to Replace an RV Plumbing Vent (and Upgrade It!)

How to Replace an RV Plumbing Vent (and Upgrade It!)

Adequate air circulation is an essential part of the design of an RV. Most RVs have several rooftop openings and items that are dedicated to the proper movement of air. At least one of these openings on every RV is an RV plumbing vent.

That’s right, not all of the vents on the roof of an RV are for keeping you, the occupants, cool and comfortable when you’re INSIDE the RV. Sure, some of them are… like the vent in your kitchen or bathroom. But others are dedicated to venting your RV’s plumbing. That’s right… your RV’s plumbing needs air, too!

So, in today’s post, we’re taking a brief look at the humble RV plumbing vent – what it does, why it’s necessary, and how to replace it (and even improve it)!

What is an RV Plumbing Vent?

In most RVs, there’s at least one pipe running from the top of the gray and black waste tanks through the roof of the RV. These are the RV plumbing vent pipes, and their purpose is to allow tank odors to be vented to the outside and to help ensure that air can enter/exit the tanks when the volume of their contents changes (like when flushing the toilet, taking a shower, or dumping the waste holding tanks). Without these vent pipes, the odors from your gray and black tanks could accumulate inside the RV, creating a most unpleasant atmosphere.

Depending on how your RV manufacturer plumbed it, your RV may have a single plumbing vent: where a single opening through the roof joins the vent pipes that come from both the black and gray tanks.

Alternatively, you could have multiple RV plumbing vents penetrating your RV’s roof, like we do, with one pipe coming from each tank to its own dedicated vent.

Either way, RV plumbing vent pipes are critical to the proper functioning of your RV’s plumbing and waste tanks. And, even more important, at the top of each vent pipe sits an RV plumbing vent cap which is attached to the roof and sealed.

Are There Different Types of Plumbing Vents for RVs?

Yes, there are different types of RV plumbing vents. And not all are equal. For instance, our RV came from the factory with the traditional kind of vent cap that’s pretty standard with most, if not all, RVs. Here’s what the average RV plumbing vent cap looks like:

Traditional RV plumbing vent

These traditional, old-style plumbing vent caps simply cover the vent opening to prevent debris from entering the pipe. But they don’t do anything at all to facilitate proper airflow.

But these traditional plumbing vent caps create no airflow whatsoever. Instead, they simply cover the vent pipes to prevent leaves and other debris from entering (or clogging) the pipe.

And in some situations, these standard RV plumbing vent caps can actually CAUSE a problem because they can direct airflow (i.e., when driving) DOWN into the vent pipe instead of up and out. When that happens, odors from your black/gray waste tanks can be forced back through the plumbing, finding their way out into the living area of your RV. 🤢

For this reason, our personal favorite RV plumbing vent cap – the one that has worked best for us since we upgraded to this type of vent in 2014 – is the 360 Siphon vent. They come in black and white, and we’ve tested them over time and (many) full waste tanks, and they’ve served us exceptionally well. We’ll get into this in more detail shortly, but for now, here’s the newest version of vents we’re referring to:

Lippert Components 389381 360 Siphon Roof Vent Cap - White (Gen 2)
  • Eliminates Odor - Exhausts Odors Out The Roof Vent Before They Have A Chance To Invade Your Rv
  • Compatibility - Engineered For A Universal Fit, The 360 Siphon Is Compatible With All Rv Vent Caps
Lippert 360 Siphon RV Roof Vent Cap
  • ELIMINATES ODOR - Exhausts odors out the roof vent before they have a chance to invade your RV
  • COMPATIBILITY - Engineered for a universal fit, the 360 Siphon is compatible with all RV vent caps

Does My RV’s Plumbing Need to be Vented?

If your RV is equipped with a plumbing system, it does indeed need at least one plumbing vent. The vents allow odors and sewer gases to vent to the outside of the RV. These vents are installed slightly above the roofline so that any breeze/wind carries off the gases and odors. And again, this applies not only to the black tank but also to the gray tank.

The gray tank contents are a concentrated (especially after a long boondocking trip) combination of water, soaps, food particles, and body oils that form a pungent liquid when combined together.

When an RVer notices a very foul smell inside the RV, it’s natural to think it must be coming from the black tank. But very frequently, what they’re smelling is an odor from the gray tank. And trust us, after a long stay off the grid, the high ratio of particles and substances other than water that form this nasty brew can make gray water smell worse than black water.

In fact, what prompted us to replace our RV plumbing vents was a foul odor coming from our gray tank after a long period of boondocking. Our gray tank was nearly full, and the odor was noticeable, especially driving down the road with the driver’s window open. This is what ultimately led us to replace our RV plumbing vents with the 360 Siphon vents.

Why Should I Replace My RV Plumbing Vent?

RV plumbing vents don’t often need to be replaced, but there are a couple of situations that would call for their replacement.

The first is age. With age comes wear and tear, damage from the sun or from low-hanging tree branches, etc. RV plumbing vents get old and can crack or break. The Dicor lap sealant around the vent can also get old and crack, allowing water to seep into the RV and cause hidden (and severe) problems with water damage.

The second reason to replace your RV plumbing vent is if you’re noticing foul odors inside your RV, either when parked or when you’re driving down the road. Again, the 360 Siphon vent is the best product we’ve found for addressing odor issues related to the RV plumbing vent.

360 Siphon RV plumbing vent

360 Siphon RV plumbing vents are designed to draw airflow up and out of the RV, helping to eliminate the potential for odors.

The design of the 360 Siphon creates a zone of negative pressure above the vent pipe, pulling air up and out of the vents so that even when you’re parked, the slightest breeze can draw tanks odors up and out of the RV. In addition, they’re made of polycarbonate, so they’re very strong and durable.

How to Replace an RV Plumbing Vent

If you need (or want) to replace your RV’s plumbing vents, you’ll probably need up to an hour or so, along with the following few tools, to complete this easy DIY project:

If you’re not familiar with Dicor self-leveling lap sealant, it’s something every RVer should carry at all times. Here’s the self-leveling Dicor lap sealant you want for this project:

Dicor 501LSW-1 Epdm Self-Leveling Lap Sealant-10.3 Oz. Tube, White, 10.3 Fluid_Ounces (Packaging May Vary)
  • Creates a secure, secondary seal along the roof’s edges, air vents, vent pipes and screw heads
  • Adheres firmly to aluminum, mortar, wood, vinyl, galvanized metal, fiberglass and concrete

Follow These Steps:

Please Note: the following instructions are from our original installation using the first generation of 360 Siphon Vent. The current version includes different instructions that require less disassembly of the old, existing vent (i.e. easier!). However, if you’d like to completely remove the old vent for a cleaner installation, these instructions are still accurate.

  1. Remove the old vent cap, which is usually held in place by a single Phillips-head screw.
  2. Use a putty knife to cut through the old Dicor, exposing the screw heads.
plumbing vent screws exposed

Cut and lift the Dicor, exposing the tops of the screws.

  1. Use your screwdriver or cordless drill to remove all of the screws (old traditional vent caps generally have six).
  2. Use your putty knife to lift and cut the old Dicor away from the roof. Note: Your RV roof could be fiberglass like ours, in which case it’s practically indestructible. But if you have an EDPM or TPO roof, commonly known as “rubber roofs,” be careful not to cut into the roof material with your putty knife… or use a plastic putty knife to be safe.
  3. After physically removing as much of the Dicor as you can, clean off the rest using mineral spirits. Again, if you have either type of rubber roof, use the mineral spirits sparingly… because soaking EDPM or TPO with mineral spirits could loosen/dissolve the underlying adhesive, potentially causing the rubber to separate from the roof.
  4. If necessary, and if you’re upgrading to a 360 Siphon Vent, use your hacksaw to trim the vent pipe down to ⅝-inch or less above the surface of the roof. Skip this step if you’re doing a direct replacement of your old, standard RV plumbing vent with the same old style (which of course you won’t be doing, right?) 😉 
using hacksaw to cut the vent pipe

Use a hacksaw to cut the vent pipe to 5/8-inch above the roofline to prepare for the installation of a new 360 Siphon roof vent.

  1. Take the small roll of sealing tape from the 360 Siphon package and remove the backing from the tape. Press it into place all the way around the base of the new vent.
sealing tape around base of vent

Place the included sealing tape around the base of the 360 Siphon roof vent.

  1. Insert the included round collar into the vent pipe far enough to allow the 360 Siphon to sit flush with the roof.
inserting the collar into the vent pipe

Seat the included collar inside the top of the vent pipe.

  1. Using the screws you removed from the old vent, reattach your new vent. Note that the 360 Siphon has only five screw holes. If the old screws were self-tapping, you should have no trouble drilling them into place even though the holes very likely won’t line up with the old screw holes (which is not a problem!). If your old vent cap didn’t use self-tapping screws, you might need to buy a few at your local hardware store. Be careful not to over-tighten the screws.
  2. Put a thick bead of Dicor around the base of the vent, being sure to cover the screw heads completely to avoid the potential for leaks.

We recommend watching the video of us installing our 360 Siphon vents. This video includes the details of our testing process, where we determined that the vents were working as advertised. The video embedded here was made in 2014, and our 360s have been performing well for us ever since. The newest version of the 360 Siphon vent looks a little different, but they install and perform the same way.

What Are the Other Vents on My RV Roof?

In addition to the vents for your RV plumbing, you’re likely to have other vents on your roof that contribute to proper air circulation throughout your RV.

Depending on the size of your RV, you could have multiple air vents that open and close, some with a fan. For instance, you may have a vent in your bathroom (unrelated to the plumbing vent) that opens to allow air in and out of the bathroom, helping to control the buildup of moisture/humidity when showering, etc. (We recommend installing a roof vent cover if you don’t already have one.)

Similarly, you may have a vent in the area of your galley/kitchen to help remove smoke odors from cooking.

Any of these vents could have a powered fan, like our Fantastic Vent Fans. Operating at various user-controlled speeds, they not only vent out humidity and odors, but they can pull fresh air through open windows/doors, helping to maintain a comfortable temperature in the RV, without running the air conditioning.

Some models of vent fans are reversible, allowing you to pull air out of the RV, or draw fresh air in. And others have a remote control so you can operate them from wherever you’re sitting. Usually, an open and running vent fan, in combination with an open window, creates a nice cooling breeze throughout the RV’s living space.

Fantastic Fan

A Fantastic Fan has a cover that can be opened to help circulate air throughout the RV.

Conclusion

RV plumbing vents aren’t often thought about, but if you ever have an issue with odor in your RV, they’ll quickly come to mind.

If you have issues with odors when your RV is parked, or when it’s moving down the road, consider replacing your RV plumbing vents with 360 Siphon vents. And as always, be sure to check everything on your RV roof regularly, to make sure that nothing is cracked or damaged, and that the Dicor sealant around all vents and other items hasn’t aged beyond its usefulness for keeping leaks at bay.

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Doug

Thursday 28th of July 2022

Hey guys, your vids are awesome, especially since we have the exact same RV as you - we've got a 2005 Mountain Aire 4304.I just bought three of these vents (using your links of course!). I have 3 of the old sharks fin rotating vents, all of which are damaged. I have a 4th vent over the rear curb side slide, it's just a cap vent. Any idea what that one is? Also, I am going to replace all the air admittance valves, I know there should be one for each of the three sinks. Am I missing any that you guys know of? I assume the washing machine using the same air admittance valve as the kitchen sink since they're next to each other? Hopefully you guys have a link someewhere for the air admittance valves so I ca use the link and get you guys some credit for that too. Great job as always, love your vids! Hopefully all these new valves and vents reduce the smells we sometimes get in the rig.

TheRVgeeks

Thursday 28th of July 2022

Hi Doug! Always great to hear from a fellow Newmar owner.... but an '05 4304!?! Tell us it isn't green with maple interior! LOL We're mystified as to why you'd have a 4th vent on the roof, since we have the identical rig and we only have 3. Ours was one of the last '05 models off the assembly line, so maybe they made a late-year change? Or maybe yours was custom-built. (Are you the original owner?) Either way, we'd replace it with a 360 Siphon vent. Coincidentally, we replaced a broken shark fin vent on a friend's Winnebago just a month or so ago, and of course installed a 360. We love our air admittance valves. Thanks for inquiring about a link. Here's the one we use: https://amzn.to/3cO85qt And yes, there should be three.... one under each sink (although maybe your rig has 4). LOL

Here's a blog post (and embedded video) we made all about the topic of air admittance valves: https://www.thervgeeks.com/holding-tank-odor-control

Thanks again for the nice comment, Doug, and safe travels - Peter & John

Bob

Friday 1st of October 2021

So the unit you installed and the unit you link on amazon are two different makes and have different install instructions. Can you clarify on the differences?

TheRVgeeks

Friday 1st of October 2021

Hi Bob. Thanks for catching that... you're right. The current version (Gen 2) of the 360 Siphon Vent comes with new (actually simpler) instructions. Seems that they have figured out a way to allow you to leave the majority of the base of your original vent in place... and just install the components of the 360 Vent that are needed to create the siphoning effect. The advantage to not removing the original base for the existing/old vent is that you don't have to worry about scraping up the Dicor, making new screw holes, etc.

The disadvantage is that you will (1) end up with the 360 Siphon Vent being raised up (just about an inch or two) above the roofline and (2) you don't have completely new parts (i.e. the old base will have X number of years of wear-and-tear and UV damage). So, if it were us... being the anal-retentive DIYers that we are... we'd likely still do the same install we originally did (in the instructions they list that on the last page as the "Complete Installation" option).

But that's us. Using Lippert's NEW instructions that allow you to leave the majority of the base from the old vent will work, too!

Hope that helps, Bob.

Mike

Friday 24th of September 2021

Something else to be aware of… odors can migrate up through the plumbing via the drains. “P” traps hold water to prevent sewer gas from seeping into the indoor environment and sometimes that water will evaporate leaving passage. Usually from sitting in storage ( I realize you guys are always on the move) and heat like the south west. If we have a washing machine, be sure to use it occasionally at least to keep it in good condition and put water in the trap !!! Simple issues we’ve solved for people over the years

TheRVgeeks

Friday 24th of September 2021

All true, Mike. Another common culprit for odor in the RV, that we've covered before, are the air admittance valves. They're unobtrusive little devices screwed onto a vertical pipe under your sinks... located between the P-trap and the gray tank. They help to make sure that the P-traps don't get drained, by allowing air to get sucked into the plumbing (like when you dump your tanks). But if they fail, they can allow odors out.

Pat Parker

Friday 24th of September 2021

I guess that is something we should replace soon..thanks for the tip

TheRVgeeks

Friday 24th of September 2021

It's a good idea to take a look at them, Pat!

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