By what do the hechsherim say, I mean those giving hechsherim that the product is produced under their certification in a way that ensures that it is not chayav tevila.
I presume that they are acting under the assumption that without their hashgacha, the products would need tevila.
What do they have to say about ensureing the supply chain is jewish owned, and do they mention this in their hechsher?