That conduit in the concrete appears in the image to be so far out of round that unless you chip away the concrete you would have a real hard time getting anything round to go into it that is the same nominal size. While I still think that the best solution is to chip away the concrete to a sufficient depth to be able to get the conduit back to round, if you are set against that concept and want to insert something you will probably need to go a size or even two smaller so that it will even fit into the conduit.
I still recommend pulling rags through to get the water out - with a larger diameter line it would take a very large amount of air to move it out with a compressor - something that a small compressor just would not do. Run a fish tape through, put in some pulling line, and then pull rags back and forth until dry enough.
You can then pull your wires, and then put them through the smaller diameter slab side conduit before sealing it in. Again, while this would not be my first choice, if you got some robust construction sealant you might be able to seal the annualar space between the conduits. At that point, I would get some concrete mortar from Home Depot/Lowes and mix up a dry-ish back and do what we would call a dry pack. You should hand form a raised area around the now protruding conduit so that water drains away from the area. I would do a conical shaped pack probably 6" in diameter and a few inches high. This will deflect water away from the area that you just sealed. Note that if the hole is in a low spot itself you will have challenges with this as the bond between the mortar and the slab is not water tight itself.
This unreinforced mortar will degrade over freeze thaw cycles and may need to be replaced periodically.
Just my $0.02.