A bath waste and overflow looks like the simplest part of a tub install — a drain, an overflow hole, some pipe between them. It is also one of the easiest parts to order wrong, because the dimensions that matter are printed nowhere on the tub, and the terminology (rough, trim, cable, linkage, schedule 40) sounds interchangeable when it is not. The result is the wrong-parts cycle: order, install day, return, reorder, rebook the plumber. Ten minutes with a tape measure breaks it. Here is how to measure a bathtub drain and overflow before you order.
What you are actually buying
A waste and overflow (W&O) is two assemblies working as one. The drain shoe sits under the tub's floor outlet and carries the visible flange and stopper. The overflow fitting mounts through the hole in the tub's end wall. A vertical tube joins the two at a tee, which runs to a standard 1-1/2 in. tailpiece and on to your trap. Kits differ in three ways that matter: how deep a tub they can span, what the piping is made of, and how the stopper operates. Get those right and the rest is finish selection.
The two measurements that matter most
- Depth to overflow centre (vertical). Measure from the tub floor beside the drain straight up to the centre of the overflow hole. Do not trust the tub's advertised depth — that figure is usually to the rim, and the overflow sits lower. Deep-soak kits exist precisely because standard ones run out of tube; the only number that counts is the maximum on the kit's spec sheet. Within an inch of it? Size up.
- Drain-to-overflow distance (horizontal). Measure from the centre of the drain hole to the inside face of the tub wall below the overflow. Most horizontal arms can be cut to length, but only down to a minimum — a very short run can be as much of a problem as a long one.
If a listing does not state its depth range, treat that as a reason to keep shopping the bath waste and overflow drains collection for one that does.
Schedule 40 or tubular?
| Schedule 40 (glue joint) | Tubular (slip joint) | |
|---|---|---|
| Construction | Thick-wall ABS or PVC, solvent-welded joints | Thin-wall brass or plastic, compression slip nuts |
| Best suited to | New builds and gut renos where piping is sealed behind finished surfaces | Retrofits where you can reach the connections afterward |
| Access needed later | No — glued joints are permanent | Yes — Canadian codes generally require slip joints to stay accessible |
| Serviceability | Cut and re-glue to modify | Loosen a nut and adjust |
If your alcove tub is being tiled in with no access panel, your inspector will almost certainly want glued schedule 40. With a panel or an open joist bay below, tubular is easier to live with. One Canadian wrinkle: most residential drainage here is ABS (black), while some kits ship in PVC (white); joining them needs an approved transition cement, so match what your house already has.
Rough-in kit or trim kit?
A full kit includes the rough (shoe, overflow elbow, tee, tailpiece) and the trim (overflow faceplate, drain flange, stopper). Opening the floor anyway? Buy the full kit and pick a trim finish that matches your tub filler. If the existing rough is sound and you only want a new look, a trim kit may be all you need — provided it matches the mechanism and manufacturer of the rough underneath. Cross-brand trim is a gamble: thread pitches, screw spacing, and stopper geometry vary enough that "universal" often means "almost."
The left-hand/right-hand myth
Bathtubs are handed; waste and overflows are not. A "left-hand drain" tub simply has its drain at the left end as you face the apron. The W&O kit itself is symmetrical — the same box installs at either end, and the direction the tee sweeps toward your trap is set by the installer, not the SKU. If someone tries to sell you a "left-hand waste and overflow," they mean a left-hand tub.
Cable vs linkage: the retrofit trap
Traditional trip-lever wastes use a lever on the overflow plate connected to a brass linkage inside the overflow tube, lifting a plunger or pop-up below. Cable-operated wastes replace all that with a rotating cap at the overflow driving a cable down to the stopper — smoother, and far less prone to out-of-adjustment plungers and hair snags, which is why brands like OS&B have made cable the default on many kits.
The trap: you cannot put cable trim on a linkage rough. The shoe and overflow fitting are shaped for the cable, so converting means replacing the rough too — a full kit, plus access below or behind the tub. If you only have access from above, the safest retrofit is a stopper-only style (toe-touch, lift-and-turn, push-to-close) that threads into your existing shoe, with the overflow plate becoming purely cosmetic. Decorative drain specialists such as Mountain Plumbing make this an easy finish update without opening anything.
The 10-minute measuring routine
- Depth to overflow centre: tub floor at the drain, straight up to the centre of the overflow hole.
- Drain-to-overflow distance: drain centre to the tub wall below the overflow.
- Shell thickness at both holes: acrylic, enamelled steel, and cast iron differ enough to affect washer stacks and thread engagement.
- Hole diameters: drain opening and overflow opening.
- Access: open joist bay, access panel, or freestanding on a finished floor? This decides schedule 40 vs tubular more often than preference does.
- Existing piping: ABS or PVC, glued or slip nuts, and where the trap sits.
- Photos: overflow plate front and back, stopper threads, and the shoe from below if you can reach it.
Write the numbers down before you browse. It is the same discipline that saves people from buying the wrong toilet — our guide to measuring a toilet rough-in before you buy makes the identical point: two minutes of measuring beats two weeks of returns.
Matching a waste to a new tub
Buying the W&O alongside a new tub? Check the tub's spec sheet for drain location and overflow height first. Deep soakers and freestanding bathtubs are where standard kits most often come up short — and on a freestanding tub the waste may be partly visible, so the exposed finish matters. Some premium brands, including Victoria + Albert and Cheviot, specify or supply compatible wastes for their tubs; when a manufacturer names a waste, use it. Still choosing the tub? Our ranking of the best freestanding tub brands in Canada is the place to start.
Frequently asked questions
Can I use a standard waste and overflow on a deep soaker tub?
Usually not. Measure from the tub floor to the centre of the overflow hole and compare against the kit's stated maximum depth. Deep soakers commonly exceed standard kits, which is why extended versions exist. A slightly long tube can be trimmed; a short one is a return.
Do I need a left-hand or right-hand waste and overflow?
No. Handedness describes the tub, not the drain kit. The same waste and overflow installs at either end; the installer orients the piping toward the trap. Only the tub itself is ordered left- or right-handed.
Is schedule 40 or tubular better for a tiled-in alcove tub?
With no access panel, plan on glued schedule 40 — Canadian codes generally require slip joints to remain accessible. With a panel or open ceiling below, tubular is perfectly serviceable and easier to adjust.
Can I replace just the stopper and overflow plate without repiping?
Often, yes — if the new trim matches the mechanism and maker of your existing rough. A stopper-only style that threads into the current shoe is the safest above-floor retrofit. What you cannot do is put cable trim on a linkage rough (or vice versa); that requires replacing the rough as well.