sew, stitch, insufficient
絀 centers on the act of joining fabric with thread: sewing or stitching. The meaning "insufficient" is a separate, less common sense that does not clearly connect to the sewing idea.
絀 combines 糸 (thread) with 出, which likely contributes a phonetic element. The sewing meaning comes from the thread component, while the "insufficient" sense may have developed separately.
The left side 糸 is thread, and the right side 出 looks like something emerging. Picture thread emerging from a needle as you sew stitch after stitch.
For チュツ, imagine a tailor sewing while chewing gum: the "chew" sound cues チュ, and the quick "ts" of the needle pulling through adds the ツ, making チュツ.