How to Inspect Pontoon Tube Seams for Leaks | Catch Small Problems Before They Become Expensive Repairs

You just pulled your Avalon out of the water after a long weekend, and as you walk past the trailer, you notice a few drips coming from the bottom of the pontoon tube — but it stopped raining yesterday, so where’s that water coming from?

TL;DR: Water inside your pontoons is bad news — it adds hundreds of pounds of weight, kills your fuel economy, and eventually rots mounting brackets from the inside out. Catching leaks early means finding them with a simple soap-and-water test after pressurizing each tube with a shop vac (not an air compressor — you can blow the seams apart). This guide walks you through the full inspection: visual checks, the bubble test, drain plug maintenance, and knowing when a leak needs a welder versus when you can patch it yourself.

Key Takeaways:

• Drain plugs are your first clue — if water comes out when you pull them, you have a leak to find
• The soapy water bubble test is the gold standard for finding pinhole leaks — but you need to pressurize the tube first
• NEVER use a high-pressure air compressor — 3-5 PSI maximum, or you’ll blow the seams apart
• Weld cracks are most common around M-brackets (where the deck attaches to the tubes)
• JB Weld works as a temporary fix for pinholes — but proper TIG welding is the only permanent solution
• One pontoon sitting lower than the other is your biggest visual warning sign

Why Water in Your Pontoons Is a Bigger Deal Than You Think

Here’s the thing about avalon pontoon boats — those Reinforced Aluminum Pontoons are supposed to be full of air, not water. But over time, even a tiny pinhole leak lets water sneak in. At first, you won’t notice. A cup here, a quart there. But water adds up fast. A pontoon tube that’s half full of water weighs hundreds of extra pounds .

That extra weight does real damage. Your engine works harder, burning more fuel. Your boat sits lower in the water, killing performance. And over time, that trapped water sloshes around, corroding the inside of your pontoons and putting stress on every weld .

One boat owner described finding water in his tube after a two-hour drive home: “Water dripping off the trailer after a 2 hour trip from the lake was a sign.”

Does your boat seem slower than it used to? Sit lower at the dock? That’s not in your head — check your tubes.

The First Sign: Drain Plugs Don’t Lie

Every Avalon pontoon has drain plugs on the bottom of each tube. The catch? They’re below the waterline when your boat is in the water. That means you can’t check for water while the boat is floating .

How to check:

1. Pull your boat out of the water onto a trailer
2. Put the trailer tongue on a jack or ramp so the nose sits higher than the stern
3. Remove the drain plugs from the bottom of each pontoon tube
4. Watch what comes out

A few drops is normal — condensation happens. But if you get a steady stream or — worse — gallons of water, you’ve got a leak .

One owner found this out the hard way: “My starboard pontoon tube/log started filling with water.” After investigating, he discovered pinhole leaks letting water in slowly but surely .

When did you last pull your drain plugs? If you can’t remember, you’re overdue.

The Visual Inspection: What to Look For Before You Get Wet

Before you break out the soapy water, do a thorough visual inspection. You’d be surprised what you can find with just your eyes.

Walk around your boat and check:

• Weld seams — Run your eyes along every single weld, especially where the deck support brackets attach to the tubes. These are high-stress areas and the most common spot for cracks
• Corners of the deck frame — Structural cracks often show up at corners. “It is usually in the back and can be caused by hitting stuff with the deck (docks, pilings etc). That racks the frame and cracks the welds”
• Dents and gouges — Even a small dent can hide a hairline crack. “Scratches and scuffs are clues. They often point to an underwater collision you might not have even noticed”
• Previous repairs — Old patches don’t last forever. Check around their edges for lifting or cracking

Pro tip: Tap along the pontoon tube with a rubber mallet. A solid tube sounds like a drum. A tube with water inside sounds dead and heavy. You can also hear the difference between an empty section and one with sloshing water .

Have you walked every inch of your pontoon tubes lately? Get down on your knees and really look.

The Soapy Water Bubble Test: How to Find Any Leak

This is the classic method that professional mechanics use. It’s simple, cheap, and works every time .

What you’ll need:

• A spray bottle filled with water and a generous squirt of dish soap (make it extra bubbly)
• A shop vac with a “blow” setting or a VERY LOW PRESSURE air source
• A helper to watch for bubbles
• A permanent marker to mark any leaks you find

Step-by-step:

1. Prep the tube. With your boat on the trailer, locate the air vents on top of each pontoon tube. These small openings (often with red plastic caps) are pressure equalization vents — they prevent the tube from building up pressure on hot days or vacuum on cold ones .

2. Pressurize — CAREFULLY. Seal your shop vac hose against the vent opening. Turn it on to “blow” and let it run for a few minutes. You only need enough pressure to force air out of any leaks — we’re talking 3-5 PSI max .

CRITICAL WARNING: Do NOT use a high-pressure air compressor. One experienced mechanic shared: “Boss has already squashed the air idea, due to a learning experience many years ago pressurizing a pontoon to make sure he had the leak welded up. He said he probably had less that 10#s when the seams let go.” Another owner confirmed: “I’ve read the toons shouldn’t be subjected to more than 3 psi or they could be damaged.”

3. Spray the soapy water. Start spraying along every weld seam, especially around bracket attachments. Hit any dents, scratches, or previous repair spots. Don’t forget the areas around the drain plugs and vents .

4. Watch for bubbles. Even a pinhole leak will produce a steady stream of tiny bubbles. Larger cracks create bigger, faster-forming bubbles .

5. Mark every leak. Once you find a leak, circle it with a permanent marker. You’ll thank yourself later when you go to make repairs.

One owner described his process: “I use a shop vac to blow air into the toon and soapy water to find the leak. It was at the bottom of a weld seam.”

Does this sound like too much work? Remember — finding one pinhole now saves you from replacing a waterlogged pontoon later.

Common Leak Locations: Where to Look First

Not all parts of your pontoon are equally likely to leak. Focus your inspection on these hot spots.

M-Bracket Welds (Highest Priority)
These are the brackets that connect your deck to the pontoon tubes. Every time you hit a wave or bump a dock, stress transfers through these brackets into the welds. Over time, cracks form .

Vertical Seams Between Chambers
Many pontoons have welded seams separating internal chambers. These are visible as vertical weld lines around the tube. Check these carefully — they’re common failure points .

Impact Points
“If you see a dent or deep scratch, spray it twice. Even a minor cosmetic scrape can hide a hairline crack.”

Previous Repair Areas
Old patches don’t last forever. Check around the edges of any previous weld repairs or epoxy patches for signs of new bubbling .

Drain Plug Threads
Sometimes the leak isn’t the tube at all — it’s the drain plug itself. Check that the plug seals tightly and the threads aren’t stripped.

Where are the brackets on your boat? That’s where you should start spraying.

Severity Guide: Pinhole vs Crack vs Disaster

Not all leaks are created equal. Here’s how to know what you’re dealing with .

Issue Type	What to Look For	Severity	Recommended Action
Pinhole Leak	Tiny bubbles, steady stream	Low	DIY patch kit or marine epoxy (temporary) / Welding (permanent)
Weld Crack	Bubbles along a weld seam	High	Professional TIG welding required
Shallow Dent	Smooth depression, no bubbles	Low	Can often be left alone or popped out
Creased Dent	Sharp lines, stretched metal	Medium-High	Consult a pro — may need welding
Gouge	Deep scratch that removed metal	Medium	Needs filling; check for leaks underneath

The critical distinction: A pinhole in flat aluminum can often be patched temporarily. A crack in a weld almost always needs professional TIG welding. “If this is a crack in the weld to one of the risers, epoxy won’t fix it. You need a guy with a TIG welder.”

What About JB Weld? The Temporary vs Permanent Question

You’ll see JB Weld mentioned on every boating forum as a fix for leaky pontoons. Does it work? Yes — but with important caveats.

When JB Weld can work:

• Tiny pinhole leaks in flat aluminum (not on welds)
• Small scratches or gouges
• As a temporary fix to get you through the season

The prep is everything: “Just be sure you prep it well. Nothing sticks to oxidized aluminum. The small wire wheels on a Dremel tool (Any small rotary tool) will get you into the tight spots. Then wipe it down with lacquer thinner or acetone and work the JB into the metal well with a popsicle stick.”

When JB Weld is NOT enough:

• Cracked welds — “If this is a crack in the weld to one of the risers, epoxy won’t fix it”
• Structural damage around brackets
• Any leak that keeps coming back

One owner who used JB Weld on an aluminum canoe said it worked fine. But for a pontoon bracket weld? “For peace of mind, do it right” — meaning TIG welding .

Is JB Weld a permanent fix? No. But it can buy you time until you can get a proper weld done.

When to Call a Professional

Some repairs are DIY. Some aren’t. Here’s how to know.

Call a pro if:

• The leak is on a weld seam — especially around brackets
• You have multiple leaks in the same area (sign of structural fatigue)
• The aluminum is torn or creased, not just pinhole-sized
• You’ve patched it before and it’s leaking again
• You’re not 100% confident in your repair

What to expect from a professional:
“Get a TIG welder to touch up the leak. Not many boat dealers have qualified welders to do much of anything on aluminum.” You may need to find a specialized aluminum welding shop .

The good news? Small weld repairs aren’t usually expensive. “It’s not an expensive repair if you pay out of pocket.”

Are you handy enough to patch a pinhole? Maybe. Are you a certified aluminum welder? Probably not — and that’s fine.

Preventing Leaks: What You Can Do Now

The best repair is the one you never need. Here’s how to keep your pontoons leak-free.

Check drain plugs after every trip. Water in your tubes means you have a leak. Address it immediately .

Inspect welds at the start of every season. Take 15 minutes with a flashlight and look at every bracket attachment .

Don’t ignore dents. That small dent from bumping the dock might be hiding a crack. Spray it with soapy water to be sure .

Store your boat properly in winter. The Avalon manual recommends shrink wrapping or indoor storage. “Mooring covers should not be used for winter storage.” Snow loads can stress the entire structure .

Rinse after saltwater use. Salt accelerates corrosion on aluminum. “If the boat is used in salt water, the engine should be flushed after each use. Also, make sure to thoroughly clean the bottom of your boat periodically to prevent salt build-up.”

How much prevention is enough? An hour of inspection each spring saves thousands in repairs.

Leak Severity and Response Chart

This chart helps you decide what action to take based on what you find.

How to read this chart: Green bars show how DIY-friendly each repair is. Red bars show how urgently you need to address it. Bracket area cracks are emergencies — don’t ignore them.

FAQ: Pontoon Leak Questions Answered

What makes Avalon pontoon boats different for leak inspection?
Avalon uses Reinforced Aluminum Pontoons with Multi-Chamber Flotation Design — each chamber has its own vent and drain, so you need to check each section individually.

How much pressure can I safely put in a pontoon tube?
No more than 3-5 PSI. Higher pressure can blow the seams apart — “he said he probably had less that 10#s when the seams let go” .

Can I use my air compressor to find leaks?
Only with a regulator set to 3-5 PSI. Better yet, use a shop vac on “blow” — it can’t over-pressurize the tube.

How do I drain water out of a pontoon tube?
Put the trailer tongue uphill, remove the bottom drain plugs, and let gravity do the work. For stubborn water, use a 1/4″ hose down the vent port and apply gentle air pressure to push water out .

What’s a temporary fix for a pinhole leak?
JB Weld works if you prep the surface properly — wire wheel, acetone wipe, then apply. But plan on a permanent weld repair later .

How can I tell if my pontoon has internal chambers?
Look for vertical weld seams around the tube. Also, multiple vent plugs on top (one per chamber) is a giveaway .

What maintenance prevents pontoon leaks?
Annual visual inspections, cleaning drain plugs, avoiding hard dock impacts, and proper winter storage .

Your Leak Inspection Action Plan

Here’s what to do this weekend:

1. Pull your boat out and put the trailer tongue uphill
2. Remove all drain plugs — see what comes out
3. Do a visual inspection — focus on bracket welds and impact points
4. Set up the soap test — shop vac on “blow,” soapy water in a spray bottle
5. Mark any leaks with a permanent marker
6. Decide on repair — pinhole? Maybe DIY. Weld crack? Call a pro

Safety reminder: Never pressurize a pontoon tube beyond 3-5 PSI. If you’re unsure, use a shop vac — it’s much safer than a compressor .

The water inside your pontoons isn’t going to evaporate. Every day you wait, that water is adding weight, killing your fuel economy, and corroding your tubes from the inside out. Catch it now, fix it right, and your Avalon will run light and fast for years to come.

What’s your favorite Avalon boat feature or on-the-water experience? Share your thoughts in the comments below.

References:

• Avalon Pontoons – Use & Maintenance Tips
• Better Boat – A Pro’s Guide to Repair Pontoon Boat Problems
• iBoats Forums – Pontoon Drain and Leak Discussion
• The Hull Truth – Pontoon Leak Repair Discussion
• Shop Floor Talk – Pontoon Pressurization Warning
• iBoats Forums – Toon Leak Testing Methods