Handy people - What best fills a pipe end with a cable in it?

We’re running ethernet cable off a building, into a conduit down the side of the building, which then goes underground and then back up to hit the side of another building.

What best fills the conduit holes with the cable coming out? Expanding caulk? My buddy used to have some sort of pliable tar-looking putty that he used to permanently water proof holes like these.

Recommendations?

My boyfriend’s answer is silicone. It’s more water resistant than expanding caulk, and it’s flexible.

A common material for sealing cable exits is Coax Seal. Similar to the putty used in automotive sealing. It never hardens and can be removed with little residue. http://www.coaxseal.com/

Duct seal - any good hardware or electrical supply store should have it
http://t.homedepot.com/p/Gardner-Bender-Duct-Seal-Compound-Plugs-10-Pack-DS-110/100212441/

One of these is the best way…

http://www.google.ca/imgres?q=conduit+entrance&start=169&sa=X&biw=1206&bih=743&tbm=isch&tbnid=vWhb9FOfCk6-TM:&imgrefurl=http://www.hardwarestore.com/metal-conduit-entrance-2678.aspx&docid=K4dy_iXq9F6JzM&imgurl=http://static.hardwarestore.com/media/product/647399_front500.jpg&w=500&h=500&ei=CiMuUv2wD8yi4AOJg4GQCQ&zoom=1&ved=1t:3588,r:77,s:100,i:235&iact=rc&page=9&tbnh=205&tbnw=197&ndsp=22&tx=134&ty=73

Yep, this way the open ends of the conduit are inside the building.