So I got this overflow second hand and want to make sure everything looks correct. I am not sure where to measure to find what diameter hose I should buy. And do I just need hose clamp and I'll be set?
That is an Aqueon/All Glass drain. It is a 1.25" hose barb connection. You can also use a Drain Flex Hose may be designated as 1"(OD PVC pipe) which is the same as 1.25" (ID Hose)