No time for myself, gales, flooding, long hours at work sorting out flooding, blocked drains, damage, dismantling trees, etc.
Best way to do it is to cheat, call for a big suction tanker:-
Then you suck all the gloop out (technical term:-"gloop"), jet the line up and down with high pressure water, stick the four-wheel-drive remote camera in and take a virtual journey along the pipe, looking for cracks, debris, roots, and collapses. In this case, there's a collapsed section and tree roots about 100 ft outside our boundary line, so it's the city's mains drainage department's job to fix it, but access might be difficult for a full size backhoe, they might need minidiggers... and the beaurocratic ramifications of crossing multiple private properties to get there....
But we've informed them of it, and given them the camera footage to show the problem, so if there's another deluge, and businesses on our site get flooded, then the claims will be against the city, not us. We can prove our drains are clear and properly maintained.
(in this last pic, you can see how the road level on one side of the building is at the same level as the rainwater gutters on the roofs. Any drain problem here can mean a big trouble inside.)