Tonneau Cover Drain Tubes: How to Route, Trim and Fix Them

Rain that runs off the panels of a flush-mount folder lands in a channel along each side rail, and the channels carry it forward toward the cab. The drain tubes take it from the front of those channels to the outside of the truck. Without them the channels empty onto the bed floor right behind the cab, and on a truck parked nose-down that corner is where the water stays.

Not every owner fits them. An MX4 bed stayed dry with the tube left off, though it hadn't seen a winter yet, and a Gator EFX owner calls theirs 99 percent waterproof without the tubes installed. We'd fit them anyway. Every install sheet we cite lists them in the box and has you attach them.

Fitting the top end takes a minute. The work is getting the bottom end out of the bed on your truck, and that changes with the generation, the liner and the cover.

Which covers use drain tubes

Most hard folders and both Retrax retractables use them. Every hard folder we've reviewed comes with tubes except the LEER HF650M, and the BAK Revolver X4s, a hard roll-up, has none in its kit. Here's what each maker says, and where the far end goes:

Same on the BAK, UnderCover and Gator folders: the end of each side rail that carries the tube goes toward the cab, which is what BAK's folding cover sheet, the UnderCover Flex sheet and the Gator EFX sheet all say, word for word on the routes. No maker here publishes a tube diameter or a trim length, so the bed in front of you sets those.

Fitting and routing drain tubes, step by step

Plan the route before the rails are clamped down. Once the cover is on, the front corners of the bed are hard to reach, and a drop-in liner or a mat may already sit over the holes you were counting on.

1. Set the rails tube end forward. On the BAK, UnderCover and Gator folders, each side rail sits flush with the top edge of the bed rail, drain-tube end toward the cab. On a Retrax, the tubes fit the canister at the front of the bed.
2. Find the exit. Look at the front of the bed for the factory drain holes and plugs. If a drop-in liner covers them, decide now whether the tube goes behind the liner, through it, or out through a hole in the bulkhead.
3. Attach the top end. On the folders, the tube goes onto the front of each side rail. Retrax's install guide has you insert each tube into the canister and turn it clockwise until the fitting clicks twice.
4. Take the shortest path out. Retrax asks for the most direct line out of the truck, and we'd hold every cover to that. Keep the run falling from end to end, with no loop or sag where water can sit.
5. Cut it to length. Long enough that the outlet clears the bed and the frame, short enough that nothing trails. A RetraxPRO XR tube left too long can back up. An angled cut makes it easier to start a tube through a tight hole.
6. Tie down the loose end. A tube dangling under the truck flaps at speed. Zip-tie it to something solid so it points down and stays put.
7. Hose-test it. Close the cover, run a garden hose along both rails, and watch for water coming out of each tube under the truck. Then open the cover and check the front corners. Do all of it from outside: never let anyone into a closed bed to look, and the UnderCover sheet warns against exactly that.

Reducers, adapters and tubes that don't fit the hole

The tube and the hole are often different sizes, and you have three ways around it: enlarge the hole, step the tube down with a reducer, or find another exit. We lean toward enlarging an existing drain hole when the install guide allows it. A reducer narrows the path, and a narrow fitting is one more place for grit to stop. A reducer is the right call if you won't drill, and it has worked: an MX4 on a 2022 Tacoma long bed drains through clear tubing and a brass reducer into the existing holes, with no drilling.

A tube pushed hard into a hole it barely fits causes its own problem. It plugs the hole for the bed's own water, and the corner puddles even with the tube working. On a Tundra MX4 the hose was too tight in the hole for water to get past, and on a 4th gen Tacoma the cover's tubes blocked two-thirds of the existing holes. Leave room around the tube, or give it a hole of its own.

Soft tubing can kink where it bends toward the hole. Bend it gently, or swap in stiffer tubing for the bend. Aftermarket tubing has worked on folders, as long as it fits the rail fitting snugly and keeps falling all the way out. On a Retrax, keep the tubes that click into the canister.

When you have to drill

Drill when no factory hole, plug or liner gap gives the tube a way out, and not before. The install guide for your part number decides where the hole goes, and the only sizes the makers here print are BAK, UnderCover and Gator's 5/8 in for the bulkhead route. Owner-reported hole sizes are truck-specific; the Maverick entry below has one.

• Look behind the panel first. Retrax's guide puts it plainly: if you drill a new hole, take great care to know about lines and anything else behind where you drill. Look under the truck before the bit touches the bed.
• Drill the plug, not the metal, where you can. Retrax says the tubes usually go out through a hole drilled in the factory bed plug. On a Gen14 F-150 Lightning, drilling the plastic plugs at the front of the bed gives a tidier fit than pulling them out.
• Treat bare metal. Any hole you drill or enlarge in a steel bed leaves a raw edge. Treat it so it doesn't rust.
• Clamps stay no-drill. RealTruck calls the Gator EFX and RetraxPRO XR no-drill installs, and the Ultra Flex no-drill on most applications, and that holds for the clamps. The drain hole is a separate decision, and on some trucks the tubes are the only reason the drill comes out.

Drain tubes by truck

• Ford F-150. Start with the sheets' three routes. With a Ford drop-in liner on a 2024 F-150, the two plugs low on the front wall of the bed are out of reach, which is the case the "behind a bedliner" route covers. On a Gen14 short bed, the RetraxPRO XR's canister also covers the front tie-down anchors and the two BoxLink holes closest to the cab on each side, so sort out tie-downs while you're routing the tubes.
• Toyota Tacoma (4th gen, 2024 on). With a 5/16 in bed drain hole and a 5/8 in MX4 tube, the choice is a drill or a barbed reducer. Rough Country's Hard Top Roll-Up, which we haven't reviewed, has a similar mismatch: its owner needed a converter to plug the drain line in on a 4th gen. Toyota's own tri-fold tubes have gone through the stock holes on a spray-in bed once cut at an angle. A nose-down rake pools any water in the front corners, so check them after the first rain.
• Toyota Tacoma (3rd gen, 2016-2023). An MX4 on a 2022 long bed drains through the existing holes with aftermarket tubing and a reducer, so try the factory holes before you drill.
• Toyota Tundra. With an MX4, enlarge the drain holes and leave the tubes long enough that the water drops clear of the frame instead of running down it. Keep the tubes out from under a bed mat, where they flatten and stop flowing. LEER's Tundra listing says its HF650M needs no drain tubes.
• Ford Maverick. Plan on drilling about a half-inch hole for a RetraxONE XR's drain hoses, or on widening one of the factory drain holes near the cab. Ford's modular drop-in liner adds work: on a Rough Country Flip Up, a hard tri-fold we haven't reviewed, taking off the liner's two side panels to reach the drain spots took nearly half the install time. A Rough Country hard tri-fold's tubes work loose near the cab now and then, so check them after rain.
• Chevy Colorado and GMC Canyon. Trim the tubes before they go in the front oval holes. On a Colorado with the factory tri-fold, tubes left untrimmed blew up in highway wind and hit the back of the cab.

For the Ram 1500 (DT) and the Silverado and Sierra (T1XX), we have no bed-specific drain advice beyond the sheets: use their routes and the install guide for your exact part.

Fixing tubes that clog, pop off or leak

A tube that has slipped off its fitting is the difference between a few drips and a wet bed, so check the fittings before you blame a seal. Here's how the failures show up and what fixes each:

The funnel joint catches people out. On an Extang Endure ALX, a hard tri-fold we haven't reviewed, the plastic funnels that join the rails to the hoses are only a friction fit, and they leaked until a bead of clear silicone sealed them. That's a joint-only fix. Silicone along the cab end of a Gator EFX does stop drips, but it glues the front panel down and you lose the quick removal.

Check the tube ends after the first few storms, after a car wash and before the first freeze. On a retractable, water a blocked tube leaves in the canister turns to ice; our retractable cover winter guide covers that. If every tube runs and the bed still gets wet, our leaking tonneau cover fixes work through the seals.

Mistakes that put the water back in the bed

• Leaving the tubes in the box. Dry for now isn't dry in a downpour. The channels still empty at the cab end, and without tubes that's onto the bed floor.
• Running them under a mat. A bed mat flattens them. A mat or drop-in liner over the factory holes blocks the bed's own drainage too.
• Jamming the tube into a hole it barely fits. The tube drains, the hole doesn't, and the corner puddles.
• Drilling before you look. Check what's behind the panel, follow the install guide's location, and treat the edge.
• A long, loose tail. It flaps, kinks or gets pulled off the fitting.
• Sealing the wrong joint. Silicone belongs on a leaking tube joint, never along the front panel of a cover that folds or comes off.

Covers that make drain tubes easy, or unnecessary

If you're buying, buy the UnderCover Ultra Flex. Its two tubes push onto the front of the rails, its install sheet gives you two ways out of the bed before it asks for a drill, and it keeps water out better than the BAKFlip MX4, with no leak spot that repeats. The MX4 uses the same kind of tubes, and on a 4th gen Tacoma that means drilling or a reducer before the first rain.

If the tubes are what you'd rather avoid, the LEER HF650M has none and costs less than the Ultra Flex on every matching listing; it won't fit a RamBox or a Ram split tailgate. The BAK Revolver X4s has none in the kit either and rolls up toward the cab, for more money. The RetraxPRO XR is the retractable we'd fit tubes to: they twist into the canister and usually leave through a drilled bed plug, and it costs the most of the four.