Reef safe plastic glue

[ed99]

I finally found the 50 gal tub I was looking for to make large batches of salt water and still fit under my tank stand. The only problem is that there are four 1/2 cm holes in the bottom for some wheels. I tried to fill the holes with silicone but I couldn't get a water tight seal. Anybody have a suggestion on what else I could try?

Thanks,

Ed