Every reusable straw sold without a brush is an IOU written against the buyer’s trust. Here is the physics of why.

The tube problem

A straw’s working surface is entirely hidden. Residue — smoothie pulp, milk, syrup — coats a wall nobody can see, in a space light barely enters.

Rinsing moves water through the middle of the tube. It does not touch the wall any more than driving through a tunnel washes the tunnel.

What a fitted brush does

Bristles sized to the bore drag along the wall itself, lifting the film a rinse leaves behind. Ten seconds, done.

Sized wrong, the brush either cannot enter or slides through touching nothing — which is why bore and brush are one specification, not two purchases.

The dishwasher question

Steel and silicone straws ride the dishwasher happily, and jets do reach through short wide bores — but long narrow tubes still deserve the brush pass first.

Bamboo skips the machine entirely: hand wash, full dry, and it stays sweet for its whole working life.

What to ask any supplier

“Does the brush ship in the set, and does it touch the wall of this exact bore?” Two clauses, one honest answer.

Ours is yes to both, on every product, which is why this site calls the brush half the straw.