Still Struggling With RV Odors? Check Your Roof Vents

Want to watch a video on this topic? Click Here: RV Holding Tank Vents.

We’ve designed this guide to give you a rundown on vents for your RV’s holding tanks. RV vents are primarily used to remove odors from holding tanks, but they actually serve multiple important functions.

This helpful guide will cover three important topics:

1. How RV Holding Tank Vents Work
2. Why RV Holding Tank Vents Need to Flow Properly
3. What You Can Do To Maintain RV Holding Tank Vents

How RV Holding Tank Vents Work

All RV holding tanks are vented, but their position and function vary based on the type of holding tank.

Black & Gray Holding Tanks

Black and gray holding tanks are typically vented at the roofline of the RV, and are usually capped to prevent debris from getting inside, and from animals building nests inside them.

They are usually 1 ½” – 2” in diameter, and allow for air to flow in and out of the tank. When liquid is added to the holding tanks, it displaces the air to prevent the holding tank from expanding. This is what allows odors to be pressed out of the holding tank as liquid is added, reducing RV odors.

To further illustrate this point, watch this video demonstration where dry ice is added to the tank and the vents are capped off, in order to show what happens when waste is offgassing (releasing trapped gases) inside of a black water holding tank.

Important Note: Under no circumstances should this experiment be replicated at home, as this is for demonstration purposes only.

Freshwater Holding Tanks

Freshwater holding tank vents are usually located in a void space inside of the RV, or vented next to the fresh water connection (where you fill the tank with water).

This is typically a ½” piece of hose which is used to help displace the air as you’re filling the tank.

How Often Should You Check RV Holding Tank Vents?

We recommend checking your RV holding tank vents anytime you are on the roof of your camper to do normal maintenance. This is typically done about once per year when you are checking the state of the sealants and the roof itself.

Start by taking the cap off to remove any lingering debris, in order to prevent clogged vents.

Types of RV holding tank vent caps:

• Windvane Style Cap
• Standard Cap
• Motorized Solar Panel Cap

Understanding the types of RV holding tank vent caps can help you know what to look for as you attempt to check your vents. Some are held on with friction when they are pressed in place, while others are screwed down and may require one or more screws to be removed in order to take off the vent cap.

How Do RV Holding Tank Vents Get Clogged?

RV holding tank vents can be blocked by different types of debris.

Black and gray water tank vents are often blocked with leaves, cottonwood fluff, dust, and other debris, while freshwater tank vents are usually blocked by spider webs or other insect nests.

In rare cases, sometimes when an RV leaves the manufacturer the vent is not fully daylighted outside of the RV, and it is simply pressed up against the roofline — in this instance, you would need to have a professional cut a hole in the roof of the RV for the vent pipe.

Where You Park Your RV May Cause Temporary Vent Blockages

Here are some common examples of blockages that happen based on where you park your RV. Common causes of RV vent blockages:

• If you are parking in a valley and there is a berm covering your RV, this can increase debris which may cause a temporary blockage in your black or gray water holding tank vents.
• If you’re parked under a tree, the leaves may cause a temporary blockage.
• If you’re a full-timer, and you’re staying in one location for an extended period of time, bird nests may have been built in or around the vent.

Signs That You May Have a Clogged RV Holding Tank Vent

Now we’ll cover some easy ways to discover that you may have a clogged holding tank vent in your RV.

Foul Odors: Black Water Holding Tank Vent Clogs

When you flush the toilet, if there is an overwhelming odor, it may mean that your black water holding tank vent is clogged and no longer allowing air to leave the tank through the roof.

This traps the foul-smelling gases inside the tank, and releases them through to the interior of the RV with every flush.

Important Note: If you are attempting to fill the tank with an onboard tank rinser or a backflush style device (Flush King), and there is a blocked vent, you do risk damaging the seals or gaskets in or around the RV black water holding tank, or in the toilet itself. This is because these are weak points, where air may be forced out due to the blockage.

Slow Tank Fill: Freshwater Holding Tank Vent Clogs

If you’re attempting to fill the freshwater holding tank, and it’s not filling up as quickly as you expected, or if you’re getting more water splashing back out of the fill tube, then you may have a clogged vent.

If air is not able to be displaced out of the freshwater tank vent, it will be trapped inside, making it impossible to fill the tank completely.

Slow Drainage: Black or Gray Water Holding Tanks

If your vent becomes fully clogged, you will experience extremely slow drainage from the black or gray water holding tanks when you attempt to dump them.

Important Note: It is possible that while draining the holding tanks with a fully blocked vent, you can actually do damage to the holding tank itself, or to some of the seals.

Full Black Water Holding Tank or Clogged RV Holding Tank Vent?

Since RV holding tank sensors can be temperamental, we’ve heard from a large number of RVers that they rely on a gurgling or bubbling noise to let them know when their black water holding tank is completely full.

However, what’s actually happening is that the water line has reached up and is blocking off the vent pipe, and that is what is causing the noise. This works fairly well, unless there is an additional blockage inside of the vent line pipe, in which case, you will still be getting this gurgling sound even if the holding tank is not completely full.

How to Clear An RV Holding Tank Vent Clog

If you suspect that you have a blockage inside one of your holding tank vent pipes, you can clear it with the following method:

Step-by-step instructions for clearing a clogged RV holding tank vent:

• Remove the vent cap.
• Run a piece of ½” PEX pipe down through the vent to clear the blockage.
• Alternatively, you can use a garden hose, and run water down the vent, which should clear most of the debris caught inside the vent pipe.
• The debris will fall safely into the gray or black water holding tank depending on which one you were trying to clear. The debris is usually easily washed out of the holding tanks during the next dump.

For detailed instructions about how to clear clogged RV holding tank vents, read our comprehensive guide: How to Fix a Clogged RV Vent

RV Holding Tank Vents: Your Ticket to Odor-Free Adventures

RV holding tank vents help reduce odors in your RV, and also help your holding tanks fill and drain properly. Blockages are natural and common, but easy to fix with our step-by-step instructions. We hope this guide was informative about how to care for your RV holding tank vents, and how they can help manage odors in your RV.

If you still have questions, or need help with your RV holding tank vents, reach out to the professional Customer Service Team at Unique Camping + Marine.