Direct answer: If mice seem to be coming in around a tub drain penetration, the usual problem is not the drain itself. It is usually an open gap where the tub drain pipe or overflow piping passes through the floor, wall, or access cavity, often hidden behind the tub shoe, overflow cover, or an access panel.
Most likely: The most likely cause is an unsealed annular gap around the tub drain piping or a larger rough opening in the wall or floor under the tub.
Start by figuring out whether the mice are using a small trim gap you can see from the bathroom, or a bigger opening behind the tub, in the wall, or from a crawlspace or basement below. Reality check: if you can see daylight, insulation, or a rough framing hole, the opening is usually bigger than it looks from the bathroom side. Common wrong move: sealing only the pretty side around the drain trim while leaving the larger backside opening wide open.
Don’t start with: Do not start by packing the visible hole with loose foam alone or by taking apart the tub drain before you know where the opening really is.
You see a gap, dark void, or movement near the drain flange or around trim pieces inside the tub.
Start here: First confirm whether the opening is only at the visible trim or continues into a larger cavity below the tub.
You remove a panel and find droppings, nesting, or a rough cutout around the tub drain and overflow piping.
Start here: Start on the access side. That is usually where the real entry opening is.
Noise or movement seems to come from the overflow cover area or the wall cavity beside the tub.
Start here: Check the overflow plate and nearby wall penetrations before assuming the drain opening is the only path.
You see a pipe penetration from the basement or crawlspace under the tub and there is a visible ring gap around the pipe.
Start here: Inspect from below first and make sure there is no active drain leak before sealing the opening.
This is the most common setup. The pipe passes through a floor or framing hole that was never properly closed after plumbing rough-in.
Quick check: Look from the access side or below the tub for a ring-shaped gap around the drain piping larger than about a pencil width.
Mice often use the bigger service cavity around the tub shoe, overflow elbow, or trap arm, not the small visible gap at the tub surface.
Quick check: Remove the access panel if you have one and look for a rough rectangular or oversized circular cutout around the piping.
The movement may show up near the drain, but the real route can be a nearby wall penetration, tub supply line opening, or framing gap.
Quick check: Inspect the wall cavity, supply line penetrations, and corners around the tub for droppings, rub marks, or gnawing.
Long-term moisture can soften surrounding material, widen gaps, and attract pests to a protected cavity.
Quick check: Look for staining, soft subfloor, moldy odor, or fresh moisture around the tub drain piping before you seal anything.
You want the real entry point, not just the spot where you happened to see movement. Tub drain trim can fool you because the larger opening is often hidden behind it.
Next move: You identify one main opening or one obvious larger cavity feeding the area. If you cannot tell where the mice are entering, widen your inspection to the whole tub bay, especially supply line holes and wall corners.
What to conclude: A visible bathroom-side gap is often just the last inch of a larger route behind the tub.
If the tub drain or overflow is leaking, sealing the opening first can hide damage and make the repair messier later.
Next move: No fresh water shows up and the area stays dry during both tests. If you see fresh dripping, stop pest sealing and repair the drain leak first.
What to conclude: A dry opening can usually be sealed. A wet opening needs plumbing repair before you close it up.
You need clean edges and a clear view of the opening so the seal lasts. Dirt, droppings, and loose debris hide how big the hole really is.
Next move: You can see the full perimeter of the opening and what solid material is available for sealing. If the edges are rotten, broken away, or too soft to hold a seal, the opening needs repair work before simple gap closure will last.
The durable fix is to close the actual penetration where the pipe passes through framing or subfloor. Cosmetic trim alone will not stop mice.
Next move: The opening is closed to solid material, the pipe still has needed clearance, and the drain assembly remains serviceable. If the opening is too large, the framing is damaged, or you cannot reach the structural side, this is where a plumber or pest exclusion contractor is worth calling.
You want to know whether you solved the entry point or just one visible gap. A quick recheck keeps you from closing up a bigger hidden problem.
A good result: No new signs appear, the tub drains normally, and the area remains dry.
If not: If mice are still active, there is almost always another opening in the same tub bay or an adjacent wall/floor cavity.
What to conclude: The job is done only when both conditions are true: no new pest activity and no plumbing leak.
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Yes, but usually not through the drain opening itself. They usually use the rough gap around the tub drain piping, overflow piping, or a nearby wall or floor penetration in the same tub bay.
Not as a first move. Foam by itself is often easy for rodents to chew and it can hide the real size of the opening. First find the structural-side gap, make sure the area is dry, then close it in a way that leaves the drain assembly serviceable.
Usually no. Most of the time the better access is from an access panel, basement, or crawlspace side. You only deal with visible trim after the hidden opening is addressed.
Treat that as a separate clue. The overflow area often connects to the same hidden cavity, but the actual entry may be beside the overflow piping, in the wall, or at another plumbing penetration nearby.
Yes, if you confirm the area stays dry during a fresh drain test. Old stains are common. Fresh drips, soft material, or a musty wet cavity mean fix the plumbing problem first.
Because the visible bathroom-side gap is often only the last part of the route. There is usually a larger opening behind the tub, below the floor, or beside nearby plumbing lines that still needs to be closed.