I'm using a small maxijet 500 pump to drain a pond. It's really struggling to drain it?

I agree with Pondlady, the pump is probably only suitable to use for a small fountain and therefore hasn't got the power to pump the water up in height (head) enough as the level of the pond goes down. If you syphon it then it will drain slowly, but it will do it as long as the outlet of the tube is at the same level of the pond or below to completely empty it, a standard garden hose can be used for that. A smaller tube will however clog up too easily and may put your pump under undue stress. Finally it all depends on the size of the pond, but perhaps the old fashioned way of bailing out with a bucket may have to do, again it's not the best solution or the quickest but it will get the water out.