I recently purchased a 125 gallon drilled aquarium that I would like to use for freshwater. Does anyone have experience plugging a drilled aquarium? There are 4 holes on the backside of the tank. 3 of the holes are one inch from the top of the tank with a diameter of 1 - 7/8 inches. The final hole is 3 inches from the top of the tank with a diameter of 1 - 1/2 inches.
I purchased 2" and 1 - 1/2" inch Oatey mechanical test plugs from Loews that can expand and contract but they do not fit the holes unfortunately. I noticed Home Depot sells different size black stoppers. For example, a 1-15/16 in. x 1-5/8 in. Black Rubber Stopper might work for the 3 larger holes. I read online that bulkheads are a possible solution, but I'm not exactly sure how those work.
I just use thick pieces of glass that cover the holes with about an inch extra all around. Then I clean the tank and patches well and use silicone to seal. I'm generous with the silicone. It's easier to use a razor blade to trim after than to deal with the results of skimping.
It's not super pretty, but it works.
"The more I learn, the more I learn how much I have to learn." ~Charles Schultz