I need to add a downspout diverter to my 3" round corrugated downspout. I have a combined sewer and storm sewer system in my basement and don't want it to overflow during heavy fast downpours when the sewer backup causes a gate valve on my sewer main to close.

When I see heavy rainstorm coming I can divert the water to a rain barrel with the drain spigot open and hose water away from the house rather than having it fill up by basement.

All the rain barrel kits and diverter kits assume a rectangular downspout or a noncorrugated round. What can I use to adapt or make a diverter fit a corrugated round ?

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  • Are you saying you have a 3" square downspout and it won't fit into the rectangular barrel lid?
    – RetiredATC
    Commented Sep 14, 2022 at 4:27
  • A picture would help. Also, what do you do if a heavy downpour happens while you're not at home? Not to derail the question, but would it not make more sense to have the gutters drain into the rain barrel all the time and leave the sewer system for the sewage? (One of the reasons many municipalities have separate systems and forbid runoff being dumped into the sanitation sewer.)
    – FreeMan
    Commented Sep 14, 2022 at 11:52
  • Why not just permanently divert to the rain barrel?
    – Huesmann
    Commented Sep 14, 2022 at 14:14
  • I should have specified round corrugated, I've updated my question to reflect that. I am trying to use a diverter adapter but they all only fit rectangular or round smooth, whereas I have a round corrugated. Commented Sep 14, 2022 at 17:12
  • @FreeMan unfortunately NYC has a combined storm and sanitary sewer so if the sewer backs up any storm runoff will flood the basement - I could just permanently redirect to a small 100 sqft patch of dirt yard 20 yards from the rear of the house but it's not much soil there so I don't think it can withstand a lot of water for a long term-drainage solution. The rest of the yard and neighbors are all concrete pavers. Not sure what the implications are to the foundation and the rest of the nearby townhouses if I permanently send my roof water there Commented Sep 14, 2022 at 17:19

1 Answer 1


I presume you're not looking for a tight seal, but a "good enough to get the water moving in the right direction" solution.

If that's correct, make several vertical cuts in the end of the corrugated pipe (in the inner most part of the corrugations, where the diameter is smallest). Using these cuts, bend the rest of the pipe inward until it fits into the opening in the diverter adapter.

If this does need to be a waterproof fit, run a couple of self-taping screws through the two fittings (for a mechanical hold - might be advisable in any case), then fill it with enough silicone sealant to make it as watertight as necessary.

  • yeah it doesn't have to be super tight but I do still want it to get the bulk of the flow - I'm using it to divert storm water surge overflow away from my storm drain pipe in my shared house sewer and storm pipes in the basement when my bacfklow preventer gate closes off the street side sewer backflow and makes my storm sewer and house sewer a closed system Commented Sep 17, 2022 at 11:33

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