Plug for use with aboveground intex swimming pools. Used to plug intake and outtake pipes when working on/removing pumps. 

I recommend printing at 35% infill. You can print with PLA, but if you leave it out in the sun, it'll warp. PETG makes it more durable. TPU makes could make it more flexible, though I have not yet tried printing it in TPU as it fit snugly on the first try. Pics provided show it side by side with the stock plug.