Product to Seal Conduit contining A/C Lines

The A/C lines from the ouside compressor to the blower unit in the attic of my two story home run through a conduit the size of a rain gutter downspout. What should I use to seal the opening where the lines from the outside compressor enter the conduit in order to keep bugs and mice out?
Replies
Duct seal. They have it at any electrical supply
Duct Seal
Thank you for the tip. I bought a package this afternoon. The sales associate said that he had used, when he worked for the phone company, to plug conduits, etc.
Duct Seal
Thank You for the tip. I bought a package this afternoon.