I am going to share a conduit experience that will "blow your mind".
Back in 68-69 time frame I was installing phones in a dept store. Keep in mind this was back in the day when it was common that jobs required the electrical contractor to provide a conduit for each phone.
Well, one of the conduits was stopped up about 75 feet into the run of a 150 foot conduit. I tried to force the fish tape but to no avail. I went to the electrician and told him his conduit was clogged. He poked around with it a few minutes and finally let loose with a few expletives. He then went to his truck and came back with a blasting cap and a roll of wire. He connected the blasting cap to the wire, taped it to the fish tape and inserted it into the conduit until it reached the blockage. He then set off the blasting cap and the blockage (pieces of concrete) came blowing out the other end. We then vacuumed the conduit to remove the residue and all was good.
When he inserted the blasting cap into the conduit I thought for sure we were going to have a blowout in the middle of the floor!
Bill
