quick note of caution
When using 'glue' in the aquarium, you need to worry about three things. The first is: Will it stick? Sometimes silicone on certain rock types doesn't work out. If you're just doing PVC and gravel, you should be okay.
Second, the issue of the 'glue' itself leaching chemicals into the water that will harm your fish. This is where 100% silicone is a good thing, in theory. By contrast, the red-label Great Stuff, while being better than the other colored labels, still leaches chemicals into the water. A lot of hobbiest use this anyway, though, since they seem to find that water changes take care of the issue.
Third, however, is the concern that additives to the 'glue' might cause problems. A lot of silicones that we can find in our local hardware store contain antimicrobial compounds that work great for keeping mold and mildew out of our bathroom, but will kill fish if used in the aquarium (even though 100% might imply that there NO additives). When you pick up silicone, make sure that you check the label to make sure it doesn't say anti-mold, etc.
If my memory serves, GE Silicone 1 is fine and GE doesn't list it for aquarium use only because of some legal concerns with (I think) some of their industrial customers. Of course, I may be all wet on this one. I think I found this little tidbit on this forum, so check it out and see what you can find.
Good luck.
