Ballast University — Installation Guide

Malibu Double Decker Ballast Upgrade (2005–2011)

How to add rear locker ballast bags to your factory hard tank system — the right way.

If you're running a 2005–2011 Malibu with factory hard tanks, you already know the stock ballast isn't enough push. The double decker upgrade ties additional rear locker ballast bags directly into your factory fill and drain system — so the stock pumps handle everything. No extra switches, no separate pumps, no guesswork.

This is what the factory should have done from day one. You're just finishing the job.

What This Upgrade Does

The double decker system connects additional ballast bags to your existing hard tanks. When your factory pumps run, they fill and drain both the hard tank and the new bags simultaneously.

You get: 900+ lbs of additional ballast capacity, faster fill and drain times (roughly 15 minutes vs. 20–25+ on most DIY setups), better wave shape, and a system that actually drains completely — no leftover slosh.

This is a cleaner, faster, more reliable setup than what most shops cobble together.

Compatible Boats

Designed for 2005–2011 Malibu boats equipped with factory rear hard tanks under the floor. If your boat has rear locker space above the hard tanks, this upgrade is built for you.

Tools You'll Need

What's in the Kit

Rear ballast bag, fill extension hose assembly, Y-fitting, inline check valve, vent overflow hose, rear link hose, hose clamps, quick-connect fittings, and zip ties. Everything you need — nothing you don't.

Empty the rear locker completely. Pull out the divider panel and set it aside — you need full access to the locker space. Then remove the trim or access cover over the factory hard tank hose connections.

Once the cover is off, you'll see the factory plumbing connections you're tying into.

Locate the two factory hose connections on the hard tank. Typically, the forward connection is the vent/overflow and the rear connection is the fill hose from the factory pump.

Remove both hose clamps and disconnect both hoses. Also disconnect the factory vent overflow hose from the through-hull fitting on the side of the boat — this is usually the forward-most through-hull fitting, but verify before you pull anything. Some model years group the through-hulls differently.

This hose connects the rear of the ballast bag to the hard tank.

Feed the rear link hose through the factory notch in the rear divider panel. Route it so it exits near the middle width of the locker, then run it along the inside of the divider panel. Secure it with the included zip ties to factory mounting points, then connect it to the rear hard tank barb fitting and tighten with a hose clamp.

That's your rear bag-to-hard-tank connection — done.

This is the more involved piece — the hose assembly with the Y-fitting, inline gray check valve, and forward bag fill connection.

Lay the whole assembly out first. Orient it by finding the Y-fitting with the open end and the loose hose with the gray check valve. Bring those two together to form the loop.

Now feed the far end of the assembly through the divider panel, routing from the engine side into the locker. Pull through until the Y-fitting is positioned correctly, with both lower hose ends accessible near the hard tank connections.

Now you're tying the new assembly into the factory fill system.

Factory fill hose: Take the factory fill hose from the stock pump and connect it to the inline check valve on the new assembly. Reuse the factory hose clamp and tighten securely.

Fill extension to hard tank: Take the open hose end from the new assembly, slide on the supplied hose clamp, connect it to the factory barb on the hard tank, and tighten.

This hose connects the front port on the ballast bag to the hard tank link line. You've got two options.

Option A — Quick Route: Leave the trim panel off and route the hose directly into the locker. Keep it low and flat.

Option B — Clean Route (Recommended): Use a 1-7/8" hole saw to drill through the divider panel. Place the hole as low and close to the corner as possible. Check clearance behind the panel before you drill. Feed the hose through for a cleaner, more factory-looking install.

Take the new vent overflow hose (the one with the inline check valve) and connect it to the through-hull barb fitting using the factory hose clamp you removed earlier. Tighten it down.

Route the hose cleanly under the gunnel, secure it to the factory harness with zip ties, and run it into the locker. This is now your new vent overflow for the upgraded system.

Before placing the bag, install all fittings: front fitting for the hard tank link, top fittings for fill and vent overflow, rear fitting for the rear link.

Place the bag in the locker and connect all quick-connect fittings. For each connection: pull the red locking ring back, push the fitting fully together, then push the red locking ring forward to lock. Repeat for the front link, fill, vent overflow, and rear link.

Secure, watertight connections on all four ports. No exceptions.

Before you button everything up, run through the checklist: all hose clamps tight, all quick-connects fully locked, hoses routed low and clean, loose sections zip-tied, nothing kinked, no rub points.

Clean hose routing isn't cosmetic — it's performance. Sloppy routing kills fill times and makes future service a nightmare. Take the extra five minutes now.

Installation Tips That Actually Matter

What You Get When It's Done Right

Compared to a typical DIY piggyback setup, a properly installed system delivers faster fill times, faster drain times, more complete draining, better bag utilization, better wave shape, and service access that doesn't make you want to rip everything out.

That's the difference between "technically works" and "actually engineered."

Need a rear ballast bag for your Malibu? We build them to fit your exact boat.

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