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Two feet above that (approx 5 feet off the ground)
I assume you mean 5 feet off the floor. That is only slightly higher (perhaps 1 foot) than the usual height of a washer stand pipe. Any washer will pump the water that high. The height of the top of the washer stand pipe is only limited by the ability of the washer to pump the water up to it. Your washer probably won't pump the water 12 feet but 5 is certainly not a problem.
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trouble with my washing machine as it appeared to be leaking from the drain just out of the machine
Then the leak should be repaired. The height of the stand pipe is not a factor.
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that the extender tube (drain tube) was not installed properly;
Unless the original hose was removed, the extension was attached washer but not properly attached, and the original hose was attached to the extension that is not logical. If the extension was not properly installed why didn't he correct it. If the extension was connected and not leaking it was installed properly
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it does appear too long (it snakes)
If it is to long, I suggest that you cut some of it off. This ain't rocket science. There are two types of washer hose. The older type which was just a black rubber hose with one end formed into a bend so that it would hang in the stand pipe (the house drain pipe), and a ribbed plastic type that can be bent into the shape needed without kinking.
Both types are attached with hose clamps. Either spring type clamps or the type that tighten with a screw. The extension should have come with a short piece of pipe that you use to connect with clamps.
Your washer leaks because the hose is not properly attached to the washer, that is it not on the discharge port of the washer pump or the clamp is not tight;
Or the hose is defective, split, busted or damaged at or close to that connection point;
Or the pump discharge port is cracked or otherwise defective.
Being a stacked unit it won't be convenient but get a plumber (or handyman)
To pull the unit out from the wall, run it and see where the leak is occurring. I am assuming that the leak is inside the washer. It could be where the hose is attached or somewhere else. It could be the pump itself. You did not specify whether or not this a new washer.
As said earlier, this isn't rocket science. Find the leak first and then figure why it is leaking and what must be done to stop it.
The height of the stand pipe and the length of the hose are not factors. You should be able to plug the hose completely and not have a leak.