basket, bucket
筲 centers on a container made of bamboo: a basket or bucket, typically used for holding or carrying things.
筲 combines 竹 (bamboo) with 肖, which likely provides the sound. It originally referred to a bamboo basket or bucket.
The bamboo top 竹 suggests a woven container, and the bottom 肖 looks like a small bucket shape. Picture a bamboo basket or bucket used for carrying items.
For ソウ, imagine a bamboo basket being sewn together with strips of bamboo: sew -> ソウ, and the basket takes shape.