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Lippert 360 Siphon RV Holding Tank Roof Vent Cap White -- LIP389381 Fits 1-1/2" and 2" Pipe

Lippert LIP389381 360 Siphon RV holding tank roof vent cap in white, 4-1/2 inch diameter polycarbonate with bug screen, fits 1-1/2 and 2 inch pipe stacks
Lippert 389381 360 Siphon RV Holding Tank Roof Vent Cap, White
 
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The 360 Siphon RV vent cap eliminates odors by expelling waste fumes through the roof vent, using an updraft design to speed waste breakdown. Fits standard 1-1/2" or 2" diameter pipe stacks.
List Price: $36.49
: $30.49
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Part Number: 389381
Manufacturer: Lippert

Quantity in Stock :25

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Lippert Fits 1-1/2" and 2" Pipe 3-Year Warranty Lippert 360 Siphon RV Holding Tank Roof Vent Cap -- White (LIP389381)

The Lippert 360 Siphon vent cap uses an aerodynamic, omnidirectional design to pull waste fumes up and out of your holding tank vent stack continuously -- even in light wind, even when your RV is parked. Replace that old flat cap and stop odors before they ever reach your living space.

Stop Holding Tank Odors at the Source

Most stock RV vent caps do little more than keep rain out. The Lippert 360 Siphon is purpose-built to actively draw air upward through your sanitation stack. Its 360-degree aerodynamic profile catches wind from any direction and converts it into a consistent updraft, pulling sewer gases away from your RV instead of letting them stagnate -- or worse, get pushed back down the stack by gusts.

The result is a noticeably fresher interior environment, faster aerobic waste breakdown in the holding tank, and far less dependence on chemical treatments to keep odors manageable. Whether you are parked at a full-hookup campground or boondocking for a week, the siphon effect keeps working as long as there is any air movement at all.

360-Degree Siphon Action

Omnidirectional vane design activates in wind from any direction, creating a continuous updraft that expels fumes rather than trapping them.

Downdraft and Blowback Prevention

Unique cap geometry blocks high-pressure wind gusts from being forced back down the vent stack -- eliminating a primary cause of indoor odor events.

Built-In Bug Screen

Integrated mesh screen keeps insects, wasps, and debris out of the vent pipe without restricting airflow or requiring separate screens.

Polycarbonate Construction

Impact-resistant polycarbonate withstands UV exposure, temperature swings, and road vibration without cracking or fading over time.

Universal Fit for Standard RV Vent Stacks

The 360 Siphon collar accepts both 1-1/2" and 2" diameter pipe stacks -- the two sizes found on virtually all production RVs and fifth-wheels. No reducers or adapters are needed for either size. The 3-1/2" collar diameter and standard 2-7/16" x 3-7/16" mounting hole pattern are designed to match the footprint of most OEM vent caps, making this a direct swap in most installations.

Direct Replacement Upgrade: In most cases the mounting hole pattern matches your existing cap exactly. You can reuse the screws from your old vent cap -- new mounting hardware is not required, though you will need lap sealant (such as Sikaflex or equivalent) to properly seal the base to your roof.

Installation Overview

Installation is straightforward and typically takes under 30 minutes:

  • Remove the existing vent cap from the roof vent pipe.
  • Clean the mounting surface and remove old sealant residue.
  • Slide the 360 Siphon collar over the 1-1/2" or 2" pipe stack.
  • Align the mounting holes and secure with the original screws (or equivalent #8 screws).
  • Apply a bead of lap sealant (sold separately) around the base perimeter and over screw heads.
  • Allow sealant to cure fully before exposing to rain.
Sealant Required: Lap sealant such as Sikaflex 221 or an equivalent self-leveling roof sealant is required for a watertight installation and is NOT included. Mounting screws are also NOT included -- reuse screws from your original cap or source #8 sheet metal screws of appropriate length.

Holding Tank Odor Control: Why Venting Matters

Holding tank odors in RVs are primarily caused by anaerobic bacteria producing hydrogen sulfide and methane gases. When those gases have nowhere to go -- or when wind pushes them back down the stack -- they find their way into the cabin through toilet seals, drain P-traps, and any loose plumbing connections. Improving the updraft through the vent stack shifts the tank environment toward aerobic decomposition, which is both faster and far less odorous. The 360 Siphon enhances this process passively, with no power, no chemicals, and no ongoing maintenance.

Maintenance Tip: Inspect the lap sealant bead annually, especially after roof work or after the RV has been stored. Polycarbonate cap and bug screen require no maintenance -- simply rinse with water if debris accumulates.
No Moving Parts, No Maintenance: The 360 Siphon has no moving parts, motors, or batteries. The aerodynamic profile does all the work. Once installed and sealed, it requires no attention beyond the standard annual roof inspection you should already be performing.

Product Identification

ManufacturerLippert Components
Part NumberLIP389381 / 389381
SKU31-0230
UPC848150037466
ColorWhite
WarrantyLimited 3-Year Manufacturer Warranty

Physical Specifications

Overall Diameter4-1/2 inches
Overall Height3 inches
Collar Diameter3-1/2 inches
Weight0.9 lbs
MaterialPolycarbonate

Mounting Dimensions

Hole Spacing (side to side)2-7/16 inches
Hole Spacing (across)3-7/16 inches
Pipe Compatibility1-1/2" and 2" diameter vent stacks

Compatibility and Fitment

Pipe Stack Sizes Accepted1-1/2" and 2" diameter (no adapter needed)
Typical ApplicationRV and travel trailer holding tank roof vent stacks
OEM ReplacementDirect replacement for most standard flat RV vent caps sharing the 2-7/16" x 3-7/16" mounting pattern
Mounting HardwareReuse original cap screws or use #8 sheet metal screws (not included)

What Is Included

Included360 Siphon vent cap with integrated bug screen
Not IncludedMounting screws (reuse original)
Not IncludedLap sealant (purchase separately -- Sikaflex or equivalent recommended)

Performance Features

Wind ActivationActivates in light wind from any direction (360-degree vane design)
Downdraft PreventionYes -- cap geometry blocks reverse airflow
Bug ScreenBuilt-in integrated screen
Moving PartsNone
Power RequiredNone -- passive aerodynamic operation
Maintenance RequiredNone (inspect sealant annually)
Important Information -- Read Before Installing
  • Lap sealant is REQUIRED for a watertight installation and is NOT included. Use Sikaflex 221, Dicor self-leveling lap sealant, or equivalent. Failure to seal properly may allow water intrusion into the roof structure.
  • Mounting screws are NOT included. Reuse the screws from your original vent cap, or source #8 sheet metal screws of appropriate length for your roof thickness.
  • This cap is designed for RV holding tank sanitation vent stacks only -- not for fresh water tank vents, drain vents, or furnace flues.
  • Allow lap sealant to fully cure before rain exposure -- cure time varies by product, typically 24-72 hours.
  • Always perform roof work safely -- use a stable platform, non-slip footwear, and follow your RV manufacturer's roof load guidelines. Many RV roofs are not rated for standing loads.
  • Verify your existing vent pipe measures 1-1/2" or 2" OD before ordering. Oversized or non-standard pipe stacks may require modification.


Faster Waste Breakdown
Designed to enhance the natural breakdown of waste, the 360 Siphon helps speed up the decomposition process inside your holding tank. By encouraging a better airflow, it reduces the need for harsh chemicals, offering a more eco-friendly and efficient solution for managing waste.

Simple Installation
Installing the 360 Siphon is straightforward and hassle-free, with no moving parts involved. It starts working right away with just a light breeze, ensuring your RV stays odor-free without a complicated setup. The cap fits 1-1/2" pipes, and an adapter is included for larger or taller vent pipes, making it a versatile option for different RV systems.

Built for Durability
Constructed from durable polycarbonate, the 360 Siphon is designed to withstand tough conditions. Its strong build ensures long-lasting performance and reliability, even in challenging weather, so you can trust it to keep your RV fresh on all your travels.


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