Yeah it can hold alright on the inside but I definitely would not encourage it as a 'water-bearing' wall or 'attachment'.

+1 to that. Would have not thought otherwise, untill i found out.

thanks guys

You can use 1/4" glass for an external overflow, you don't need anything thicker. 1/4" glass is cheap enough to void any reasons for using acrylic.

might be too thin i think. just in case i bump into it. probably going with 3/8.

Lot's of tanks are made from 1/4", unless your overflow is bigger than 40 gallons I wouldn't worry about it.

thanks