10/09/2026
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Ever seen a perfectly clear strip drain suddenly stop taking water? 💧
This is something we occasionally see with very shallow tile-insert strip drains, particularly around the 21mm range, combined with a high-flow shower.
The drain itself isn’t necessarily blocked.
As the shallow channel fills, the water can reach the underside of the tile-insert cap. With such a small clearance around and underneath the insert, the pathway for water to enter the channel — and for displaced air to escape — can become heavily restricted.
The result? Water starts backing up across the shower floor and you’re suddenly standing in a puddle, while the drain appears to be taking water extremely slowly.
Technically, linear-drain manufacturers recognise that the grate or tile insert can throttle the intake of water into the channel, and hydraulic performance depends on things like the available opening, water head, outlet capacity and shower flow rate.
Our simple fix: raise the tile insert slightly.
We install small self-adhesive feet underneath the tile cap. This creates a little more clearance beneath and around the insert, giving the water — and displaced air — a much easier pathway into the channel.
That tiny increase in clearance can completely eliminate what we commonly refer to on site as a “vacuum lock.”
Where possible, we prefer not to use extremely shallow 21mm tile-insert strip drains, particularly with high-flow showers. But when the drain is already installed and this issue presents itself, this is a simple solution we’ve found works extremely well.
Sometimes a few millimetres makes all the difference. 👌
