One way is to have the tube fully extended, hold it at opposite ends (cap on) and, holding it taut, run it from bottom to top over a sharp-edged corner of something (laminate worktop end is useful). This forces the contents ahead of the load point (the worktop's corner line) from bottom toward the top. Let any air out by taking the top off and squeezing the contents upward after the first pass, re-close the tube and repeat. This of course works with any flexible tube - but it must be intact, otherwise the contents will be forced out from any break.