FAQS - RV Vent Caps

If you are uncomfortable with working with the roof membrane and water sealants, please see your local RV service center. If you are comfortable with the above then yes!  See our printable 360 Siphon™ Installation Instruction Sheet for details.

Yes, parked or travelling, this roof top vent eliminates all fumes and gases from the holding tanks.

Yes, here is a video that explains how all of our products work.  Please note that this is a QuickTime Movie that is approximately 5.5MB so will take a minute or two to load. Click here to view our video.

Tank fumes seep into the RV thru seals and dried out traps due to a higher air pressure inside the tank than in the RV.

Cleaning the tank won't help because it’s purpose is to hold waste (waste is always dirty and stinky). Adding more odor masking agents will camouflage the fumes and gasses so it smells 'perfumey', but you are still inhaling methane, ammonia and other gases.

Due to wind direction. Conventional vent caps cannot handle turbulent wind which is caused by obstacles on the roof top. Depending on wind direction, updrafts and down drafts hitting the vent cap will be forced down the stack pushing fumes out of the tank. Odors will be drawn out of the tanks if a lower pressure exists in the RV than the tanks, this can be the result of certain RV doors or windows open in the relation of the wind direction. The solution to this is to maximize all wind available to create a lower pressure in the tank in all situations.

This due to the open window causing a lower pressure in the RV than in the tank. This is why it is important to have a vent cap in place that will insure a lower tank pressure.

Again, its due to a high pressure in the tank now having no blockage at all to drift into the living space.

Very unlikely. All RV toilets have a small ½” overflow tube that connects the tank to the underside of the rim. Its has a slight design of  a water trap but its usually dry. You can’t stop fumes under pressure.

In some cases the gray can be worse than the black, again the water traps often dry out due to vibration and heat. The soaps and grease that accumulate in a gray tank can get quite rancid.

Lower air pressure existed in the RV than in the tanks.

Due to the fume build up, tank gasses will not come out on their own, if they are drawn off during travel and daily use the odor level is much lower.

Its aerodynamicly engineered, it has no wind resistance; it channels wind into is vortex where it creates a low pressure at the exhaust port. The lid is a complex series of shapes that has taken 3 years of design and field testing. The siphon cannot fail, it’s the worlds only non-mechanical air check valve that eliminates stack down drafts and creates a low pressure in every possible wind direction.

It does two important things to your sewer system.  It is always drawing off odors and gasses out of the tanks so fume build-up does not occur.  (Tank fumes are heavier than air and will not come out on their own.)  In addition, it creates a low pressure in the tank in all wind conditions.


The difference in the performance is a 15 - 18% higher draw rate on the Gen 2 as opposed to the Gen 1. Two noticeable differences are in the size and configuration. The Gen 1 is wider and taller and had a dome shaped top. The Gen 2 is significantly smaller and has a concave top. The footprint of the Gen 2 is 3 15/16" in diameter.  Another important feature, is the ability to take advantage of the existing debris cover that manufacturers install.  If the base is not deteriorated the cap, can be removed and the siphon simply glued directly to the pipe. The advantage of this is that the owner doesn't have to disturb the sealant on the rooftop.


Yes, it works even in the slightest breeze, stationary or driving.

If there is no wind there will never be a problem, air pressure differential cannot happen, so odors will not exist.

In some cases it can work extremely well. It depends on the problem you have, but if on those windy days that sewer odors are present, its almost certain the Siphon Stack Cap will work. Also works well on outhouses.

Composting toilets are designed to draw off the moisture by venting out through the vent stack. Down drafts and extra moisture or rain is definitely not wanted. The Siphon stack cap does both as well as keeping out other airborne debris.