question for ebb and grow users

I was only using 1 outlet on each side of the controller bucket to start with. I had a small piece of tubing looping the 2nd and 3rd outlets back to the bucket. I now want to use another outlet. How do you close off one outlet? The directions say to use a zip tie but I could never get that tight enough to stop all the water.

Thanks!

They have rubber plugs at Home Depot that works for that.

I couldn't find a rubber plug but I did find a plastic plug that seems to work well. Thanks for the suggestion.