I've not used this, but from the pictures the wastetrap material looks like the stiff carbon impregnated sheets used in some other filter solutions. Those are fairly stiff so they will slide into the frame easily. Getting anything else in there might be a problem.
My personal solution to this issue is making sponge inserts that are held in place by plastic needle point 'canvas'. The plastic sheet fits in the retention groove and keeps the sponge from blocking the outflow or floating into the outflow.
My personal solution to this issue is making sponge inserts that are held in place by plastic needle point 'canvas'. The plastic sheet fits in the retention groove and keeps the sponge from blocking the outflow or floating into the outflow.
