Plugging a hole in return line

[T828k]

27 Pack (10 Assorted Sizes) 000# - 7# Tapered Lab Bungs Solid Rubber Stoppers https://a.co/d/72WT6wo

Hopefully the link works, the previous owner of my tank drilled holes in the return line behind the weir/overflow, would those rubber plugs be reef safe? I'd like to plug the holes as a lot of already filtered water is flowing right back into the sump, worst case is I have to rebuild the return pipe but I'd much rather not go that route.

 

[exnisstech]

Sounds like they may have drilled them for syphon breaks. I drill them in all of mine. Got a pic?

 

[T828k]

Sounds like they may have drilled them for syphon breaks. I drill them in all of mine. Got a pic?

I don't have a pic but yes they are siphon breaks I'd have to keep the returns close to surface if I plug them but I just think a lot of "clean" water is being sent right back to the sump

 

[exnisstech]

You may want to make sure the sump can handle the back flow with the pump off if you plug them. If you plug them then the water is going to drain all the way down to the end of the return nozzles. The deeper they are the more water will drain before the syphon breaks and may overflow the sump. Also not sure why you wouldn't want the returns close to the surface. They are good for surface agitation and keeping dust and skum from settling on the surface.
With out seeing what you actually working one and the size of the holes I doubt anyone can answer your original question.

 

[Malum Argenteum]

"Enjoyist" brand plugs made of "Permium Rubber". Not likely a product made with attention to low levels of leachable chemicals. Maybe try a nylon hex bolt?