approved rain leader/downspout/conductors Home › Forums › Public Forums › Drainage & Sewerage › approved rain leader/downspout/conductors This topic has 1 reply, 2 voices, and was last updated 20 years, 11 months ago by DUNBAR. Viewing 1 reply thread Author Posts 7 Dec 2003 at 6:34 pm #279357 MasterPlumbersKeymaster Miliwaukee inspector says I can’t use plastic corrogated for a downspout. I can’t find specs in IBC. Please let me know. 7 Dec 2003 at 9:28 pm #300624 DUNBARParticipant If this is a commercial application, then cast-iron is required with accessible clean outs. Minimal distance of downspout into cast-iron is a inch. Plastic corrugated is proven to be junk and will collapse easily underground with just a small amount of dirt above it. Good luck. That will be a drain line replacement someday soon. Author Posts Viewing 1 reply thread You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In