The invention includes a method of using a cap containing an internal thread form matching an external thread form on a flexible throat for a collapsible tube enclosing at least one contained product. Twisting the cap engages the internal thread form and the external thread form. These collectively urge the cap and the flexible throat to seal the contained product into the collapsible tube. Deforming the flexible throat through squeezing the collapsible tube dispenses essentially all the product. The collapsible tube may preferably include an external thread form on a flexible throat coupled to a flexible shoulder. The external thread form mates to a cap with an internal thread form urging the flexible throat to seal against the cap when the cap is twisted onto the flexible throat. The flexible throat and flexible shoulder flatten to dispense essentially all of the product.