I have used the colored ones full of water over long periods of time. The only problem I have had is that certain dimensions (taller ones) bow out pretty bad when full. I would not trust them if you wer to drill a hole for a bulk head.
I found a great alternative that is VERY durable but does cost a little more. Farm supply stores carry water containers for animals that can be bought in several sizes. I know someone that is using 3 100 gallon ones for 2 500 gallon saltwater tanks that are connected. The ones I am talking about, I have seen them made of fiber glass and plastic and RubberMaid even makes them. They are thick and very durable and you can drill holes in them for bulk heads. They make really good sumps. You should be able to get them at any farm supply store and I think Grainger also sells them.
Here is a pic of what I am talking about.
http://www.skippysstuff.com/biofil01.jpg
I found a great alternative that is VERY durable but does cost a little more. Farm supply stores carry water containers for animals that can be bought in several sizes. I know someone that is using 3 100 gallon ones for 2 500 gallon saltwater tanks that are connected. The ones I am talking about, I have seen them made of fiber glass and plastic and RubberMaid even makes them. They are thick and very durable and you can drill holes in them for bulk heads. They make really good sumps. You should be able to get them at any farm supply store and I think Grainger also sells them.
Here is a pic of what I am talking about.
http://www.skippysstuff.com/biofil01.jpg
