1L round heatproof jar

Proper commercial grade glass, thick and heavy, so it stands up to years of refilling rather than chipping after a few months. For perspective, it holds around 1kg of washing soda. Tested with boiling water without cracking, so Laundry Butter cleaning paste can be mixed straight in the jar and left to set. Food grade and non porous (the glass has no tiny holes for smells to hide in), so it won't hold onto colour or essential oil fragrance. The jar handles the dishwasher fine. Wash the lid by hand so it doesn't rust.