Remember to leave an extra pull line in the conduit when you're done.

I always leave several.

Shop vac and an appropriately sized foam rubber ball (with the first
small pull string run through it) is one standard approach to the
conduit problem, at least for empty conduit needing the first string run
through. I suppose that compressed air at the feed end could also be
used, but the shop vac at the far end is what I'm familiar with being
actually used, and it seems easier to seal on.

If there won't be idiots working in the conduit (and it there are,
nothing will help as they'll yank out the extra pull strings, too) you
can run a loop a few feet longer than the run and pull new wires without
"using up" a pull string.

--
Cats, coffee, chocolate...vices to live by