Trying to access overflow box to fill gaps

[Johnbarmy]

Ok long story, I have to 2 overflow boxes im trying seal and secure i got weldon 4 and attached them but they have gaps in them so i tried filling in gaps with silicone yesterday I hooked everything up and the tank filled about 3/4 and the silicone gave in causing water to flow through the gaps....im trying to figure out if i cut out the top of acrylic tank just over the overflow section to silicone the insides or is there another way to fill the gaps.....

 

[Johnbarmy]

I'm wanting to cut just the corner out to access the overflow box

 

[OhMatic]

Johnbarmy
If your working with acrylic do not use silicone. Silicone will not work.
Use weld on #4 or weld on #16.
#16 is more viscus than #4.
#16 has a consistency more like elmers white glue than #4

 

[Bogue Chitto]

You may check on supermend. I have used that to fill in a hole in the bottom of a glass tank and it worked great. It will bond to acrylic too.