With Intamins there are very obvious plugs on the support walls that they remove and put the sand in, as the supports are sealed on both ends as well. I guess I could not be lazy and actually go to IOA and see what I can of the supports and track that are up and see if I notice any obvious plugs. But...nah, I'll let someone else do that.
EDIT:
This picture shows what the plug looks like on Intamin supports.