Are the pipes straight?
If you have a perfectly straight shot you can sometimes put a rag on the end of a stick and push it through.
But the insides of the pipes can be a collection of calcium buildup, calcerous worms and featherdusters and sponges. These things are glued to the inner wall of the pipe and they just won't wipe off, Even if you soak in vinegar you will probably get less than 30% to break loose.
If this is an old system with old plumbing - 10+ years and you are worried that there has been enough growth to impede the flow of water, then when the sump comes out replace the pipes.
Dave B