I just don't think that given the extreme sensitivity of the average reef system that this is anything you want to take a chance on. There's not much that you need ABS for that you can't make due with PVC. Until I hear from a manufacturer of ABS that the product is safe for reef use (or at least for potable water use) I just wouldn't take the risk. It reminds me of the shortcut I used to a quick reef via lava rock. I thought I had a cheap solution to providing mass to my reef, turns out it was what ultimately came to be the cause for my perennially low pH. Once I got it out the pH shot up from 7.8 to 8.4 You may get away with ABS with no visible issues, but then low viability in a fish or invert is a lot to risk for some plastic pipe whose primary function is moving human waste.