I understand the problem with your son and all. I just thought you didn't want to return it because of the money issue as you mentioned the guarantee and discus are usualy quite expensive fish. I don't blame you for any of the mistakes you have made. We've all made them before. It's inevitable when LFSs etc don't provide you with good advice to start with. Sorry if I sounded otherwise it's just very frustrating.
Anyway use the vacuum to take water from just above the gravel. It should also suck up any fish waste. However, don't stir up the gravel too much.
You didn't say whether you know about cycling or not so I'll explain it anyway

. Basically, fish produce waste. The waste contains ammonia. Ammonia is highly toxic and poisons fish. After about a week of this ammonia being in the tank, good bacteria start to grow which feed on it. They convert ammonia to a slightly less harmful compound called 'nitrIte'. NitreIte is still very poisonous. A little while afterwards, another kind of good bacteria also starts to grow. It feeds on the nitrIte and turns it to nitrAte. NitrAte is not realy dangerous but should be kept under 20ppm (get a test kit) or at least under 40. Because you have the discus, I'd actualy aim to keep it very low indeed. The only way to remove nitrAtes effectively is by doing regular partial water changes.
Now the thing you must know about these good bacteria is that they live in your tank's gravel and in the filter's media (sponge or whatever). Chlorine and anti-bacterial medications will kill them. The reason I said not to stir the gravel up too much before is so you don't disturb the bacteria at this crucial stage. Similarly, it is vital that you NEVER use water straight from the tap unless you have used a de-chlorinator in it first. Also, because the bacteria colonize your filter, you must avoid changing the media. If it becomes clogged, take the media out and rinse it carefuly in some old tank water - again, if you use water right from the tap without de-chlorinating it first, you'll kill off the good bacteria.
About the cycling process - ammonia goes to nitrIte and then nitrIte is converted to nitrAte. I've already mentioned that a nitrAte level under 40ppm is safe for most fish (keep it lower for discus). Safe levels for ammonia and nitrIte are strictly ZERO. You shouldn't have ANY of these substances in your tank. If they are there, you should do a water change.
Just to make something clear, I think we would agree that the fish' lives are a priority. Normaly, a full cycle would take about 6 weeks, when you are doing daily water changes to keep ammonia and nitrIte at safe levels for fragile fish, you are also depriving the good bacteria of a lot of food. They'll still multiply but more slowly. Just be aware of this. It may take longer than usual. I didn't mention it before.
Oh and something you might find useful and would save you a LOT of trouble - ask your LFS for some old filter media and gravel right from one of their established tanks. It will contain a good amount of the good bacteria and that should get your own colony going. It could make the cycle almost instant if you're lucky!