Easy Freestanding Tub Installation (Island Tub Drain Rough-In)
- Isaac Ostrom
- Dec 18, 2025
- 6 min read
Updated: Dec 29, 2025
Alright, so today we’re talking freestanding tubs, and more specifically, how to rough one in the right way when you don’t have access from below.
This is one of those situations that gets a lot of people — homeowners and pros — in trouble if it’s not planned correctly. Freestanding tubs look clean, modern, and high-end… but behind that clean look is a little bit of plumbing strategy that has to be done before the tub ever shows up.
If you’re on a second floor, on a concrete slab, or anywhere you can’t just crawl underneath and hook up the drain later, this rough-in method is not optional. You either do it this way, or you’re cutting drywall, patching ceilings, and regretting your life choices.
So in this post, I’m going to walk you through:
Why freestanding tubs changed how we rough in plumbing
The exact rough-in kit you need (and why)
How to set this up so the tub literally drops into place later
Pipe sizing, transition glue, measurements, and tools
And why this saves a ton of time, money, and stress
This is one of those “do it once, do it right” setups. Let’s get into it.
Key Takeaways (TL;DR for Homeowners & Pros)
Freestanding tubs must be roughed in from above if you don’t have access underneath
This setup is critical for upstairs bathrooms and concrete slabs
The rough-in kit allows you to drop the tub in later without touching plumbing
Pipe height and measurements matter — guessing will burn you
You’ll need a PVC-to-ABS transition cement (this is non-negotiable)
An inside pipe cutter is one of the most valuable tools you can own
Done right, the tub installs in minutes with zero ceiling damage
Why Freestanding Tubs Changed Everything
Back in the 80s and 90s, bathrooms were full of big drop-in tubs. Jacuzzi decks, giant platforms, tubs built into framing — that was the look.
Those tubs were easy from a plumbing standpoint because:
Everything was accessible
The tub deck hid mistakes
Plumbing could be adjusted later
Fast forward to today.
Now everything is:
Freestanding
Open
Minimal
Exposed
Which looks great… but it means you don’t get a second chance on the rough-in.
Most of the bathrooms I work in now — especially remodels — are upstairs. That means no crawl space, no basement, and no access underneath once the ceiling is closed.
So if you don’t plan ahead, your only option later is:
Cutting drywall
Patching ceilings
Matching knockdown texture (good luck)
That’s why this rough-in method exists.
The Big Problem: No Access From Below
If you can’t reach the drain from underneath, you cannot hook up a traditional freestanding tub drain after the fact.
That’s the mistake I see people make all the time.
They think:
“We’ll just set the tub and connect it later.”
Nope. Not happening.
Once the floor is finished and the tub is sitting there, you’re done. There’s no room to glue fittings, tighten connections, or adjust height.
So the solution is to rough everything in now — perfectly — so the tub can literally be dropped into place later.
The Rough-In Kit You Need (This Part Is Key)
The kit I use — and the one shown in the video — is the Jacuzzi MZ 20000 Rough-In Kit.
This kit is designed specifically for freestanding tubs where:
You don’t have access from below
The connection must happen from above
The tub drain needs to slide into place
What Comes in the Kit
This is what makes it different from standard tub drains:
A downspout that connects to the tub drain
A floor-mounted rough-in fitting
A slip-fit rubber coupler inside the fitting
A protective cap (the red piece) to keep debris out during construction
That rubber coupler is the magic.
Later — when the tub is ready — you:
Lube the pipe
Drop the tub straight down
The drain pipe slides into the rubber coupling
Done
No glue. No crawling underneath. No drywall repair.
Understanding Pipe Sizes (Don’t Skip This)
Here’s something that catches people off guard.
The rough-in fitting is 2 inches.
But most tubs drain into 1-½ inch ABS.
That means you must supply your own reducer bushing:
2” to 1-½”
ABS side for the house plumbing
This is normal — just don’t miss it when ordering parts.
PVC to ABS: You Need Transition Cement
Another super important detail.
The rough-in fitting is PVC.
Most residential tub plumbing (at least where I’m at) is ABS.
You cannot glue PVC to ABS with standard cement.
You need:
PVC-to-ABS transition cement
This glue is thinner, more watery, and specifically made to bond dissimilar plastics. If you skip this and use the wrong glue, it will fail.
I always coat:
The inside of the fitting
The outside of the pipe
No shortcuts here.
The Most Valuable Tool for This Job
Let me say this clearly:
An inside pipe cutter is one of the most valuable tools you can own if you do remodel work.
This tool:
Attaches to a drill
Cuts pipe from the inside
Allows you to cut pipe flush with the subfloor
Saves you from crawling under floors or cutting ceilings
We use this tool all the time — not just for tubs, but also for shower drains.
When plumbers ask me:
“How do I know where to cut the pipe?”
I tell them:
“Just bring the stub-out up. I’ll handle the height.”
This tool is how.
Measuring Pipe Height (This Is Where People Mess Up)
Once your reducer bushing is glued in, you can take accurate measurements.
Here’s how I do it:
Measure from the top of the subfloor to where the pipe needs to stop inside the rough-in fitting
Account for how far the pipe inserts into the fitting (in this case, about ¾”)
Use the full fitting height to calculate your cut
In the video, that measurement worked out to 3-¼ inches.
Once you know that number:
Mark your inside pipe cutter
Cut slowly
Double-check the fit
You want the fitting to sit perfectly flush with the subfloor.
Not proud.
Not low.
Flush.
Cutting the Pipe From Above
This is where the inside pipe cutter shines.
Instead of:
Crawling under the floor
Fighting a hacksaw
Making a mess
You just:
Insert the cutter
Spin it with the drill
Pull the pipe out clean
It’s fast, accurate, and clean.
Just make sure the cutter is tight in the drill. If that bit falls into the trap, you’re having a bad day.
Gluing the Final Connection
Once the height is right:
Use ABS cement (not transition glue here)
Coat both the pipe and fitting
Press together firmly
Orientation doesn’t matter — it can rotate any direction.
At this point, your drain height is locked in.
Securing the Rough-In to the Subfloor
The manufacturer shows screws in every hole.
Personally?
That’s overkill.
I secure it solidly, but I don’t go crazy. The goal is:
No movement
No flex
Solid connection
Once this is screwed down, the plumbing side is done.
Why This Method Matters So Much
Let’s talk real-world consequences.
If you don’t do this:
You’ll be cutting ceilings
Patching drywall
Trying to match texture
Dealing with paint touch-ups
Wasting time and money
Ceiling patches never look perfect — especially with knockdown or orange peel texture.
This rough-in eliminates all of that.
Later, when the floor is finished and the tub shows up:
Lube the pipe
Drop the tub
Walk away
That’s it.
What Happens Next?
This video and post are rough-in only.
The next step — which I’ll show separately — is:
Setting the tub
Sliding the drain into the rubber coupler
Making final plumbing connections
But if this part isn’t done right, none of that matters.
Common Mistakes to Avoid
Forgetting the reducer bushing
Using the wrong glue
Guessing pipe height
Not cutting flush
Trying to hook up the tub afterward
Every one of these mistakes costs time and money.
FAQ Section
Q. Can I do this on a concrete slab?
Yes. This method is perfect for slab foundations where there’s zero access from below.
Q. Do I really need transition cement?
Yes. PVC to ABS requires transition cement. Anything else is wrong.
Q. What if my pipe height is off?
If it’s off, the tub won’t seat correctly. That’s why measuring and test-fitting matters.
Q. Is this only for Jacuzzi tubs?
No. The rough-in method applies to most freestanding tubs that use a slip-fit drain system.
Q. Can homeowners do this themselves?
If you’re comfortable with plumbing, measurements, and tools — yes. If not, hire it out. This is not the place to guess.
Final Thoughts
Freestanding tubs look simple — but the plumbing behind them is anything but.
This rough-in method:
Solves access issues
Prevents ceiling damage
Makes installation clean and stress-free
Works for upstairs bathrooms and slabs
If you’re planning a freestanding tub and you don’t have access from below, you need to do this. There’s no workaround that’s cleaner or safer.
And hey — if you found this helpful, share it, subscribe, or drop a comment in the Tile Coach Forum. I love seeing you guys out there learning new trades and building stuff with your own hands.
I love being your Tile Coach.
We’ll see you in the next one.