Blocking Up Tub Outlet

[MickR33]

Hey i have a 45ltr hydroponics resivoir tub that has 2 x 32mm tub outlets on it, one on each side and i want to relocate one of them and put it on the other side a few inches from the other outlet. I want to do this because it will be better for the way i will be plumbing it up, if i dont move it i will have to use a couple of elbows to get it to the other side and it would be best not to use many elbows when it can be avoided. My problem is what to do with the 32mm hole left in the tub when i move the tub outlet, originally i was going to leave the outlet there and use a short piece if pipe with an end plug in it so it will be blocked, and then i would just buy another tub outlet to use on the other side, but i would like to be able to not have a bit of pipe sticking out of the end of the tub if i can, so i have been searching for some kind of fitting that blocks the hole but i couldnt find anyone that makes one. It would be so simple for a company to make one.
So does anyone know of any fitting that is made to block a 32mm hole in a tub?
What other ways could i do this? i was thinking i could get a square piece of plastic and put some waterproof silicone around the hole on the inside of the tub and put the square on it and let it dry, that would do it but i would love to just be able to put some kind of fitting in there to block it off though.
So what are your thoughts?