I've read various threads that seem close to being on point but... Daughter just bought a house. Rats in crawl. I've checked all vents etc. and inspected crawl thoroughly. The only intrusion I discovered was a 4" ID drain line that starts at ground level on the outside of the foundation wall (like you were going to drop a downspout into it except it's on the gable end of the house), goes into the dirt, cored through the foundation (concrete foundation, not cinder block) maybe a foot to 2 feet down from grade and then runs another 5 feet into the crawl and terminates with an open end. Obviously a rat highway not to mention water depending on rain/wind direction. Looking for the best way to plug this decent sized hole permanently understanding that it will be in contact with soil on the outside. Crawl is fairly skinny on this side but can get there and could put something on the inside (e.g. PL3 a cement board to the inside to serve as temp form) but not sure on proper materials/method including sealer since outside soil contact. Any advice appreciated.

Follow-on to provide more info: Included pic of my downspout drain line. It looks identical (same drain pipe type, same ID/OD) to my daughters setup except no downspout gutter and no reason for there to ever to have been one in this location. No evidence of there having been AC, no electric running in the crawl in the area. Don't believe it could be for ventilation, the crawl is well ventilated including two vents very close to the location of this. Example pic

  • Is this drain line a pipe? If so the easiest might be just to add a cap on the outside. Problem is this might be for venting.
    – crip659
    Apr 16, 2023 at 14:25
  • They make caps for those pipes. They are known as Big-O up here, not sure if that is a maker or just what people call them.
    – crip659
    Apr 16, 2023 at 17:53

1 Answer 1


That sounds like a chase for some utility. Most likely the lines and wires for an AC system.

You probably want to leave it intact for possible future use. Capping is the best answer to the problem. You didn't say what material the pipe was, so there can be different options. PVC glued with a cleanout cap inside and out is one. What you don't want to do is cap with a material that the rats can easily chew through, like rubber or nylon.

Of course the simple solution is to fill it with cement, but that prevents any future use. What it was intended for is a moot point since it is not being used.

Tell us the material to get more suggestions.

EDIT: The pic now provided shows corrugated drain pipe. Unfortunatly the caps are soft plastic that rats can chew through.

I would dig down about 8 inches around the pipe. cap with a PVC end cap glued on with a construction adhesive and leave that end buried in the ground. Then cap off the end under the house with another cap taped on or with screws to hold it on and call it done.

  • Thanks for the help! I think I found a polyethylene cap that screws on at HD that I will also add some construction adhesive to (both sides). When I dig it up, I will see if it's perforated and deal with that with some sealant or something.
    – ScottM
    Apr 16, 2023 at 19:44

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