You could possibly have some condensation issues, which I had not considered. I'm also not terribly familiar with Fluval's line of tanks. If they are not completely covered, this of course would be a bigger issue. You might try sticking a bucket of water filled and placed so that the water line is at the same height as the waterline would be in the tank to see if you observe any condensation. That way, I would think you could remove the bucket prior to causing permanent damage and without putting a whole lot work into installing an aqaurium you would have to take down.
As far as the Python parts go, there's really not much to fail on them. The only parts I've ever replaced in the 20 years of owning one are the faucet adaptor and the pump. Being plastic and generally connecting to metal, the plastic will stretch and threads will strip over time leading to a failure. The faucet adaptor you should be able to get at any hardware store. The pump is the same as a waterbed drain and fill kit that you can pick up at most hardware stores as well. (I'll admit, these have become rarer in recent years as waterbeds don't seem to be as popular as they once were.) The piece you need is on the right in the picture below. The top part connects to a water source and your drain hose connects to the male fitting pointed to the right. Water pressure creates a venturi to start a siphon. And will drain the water through the bottom portion of the unit. (If your tank is pretty high, you can probably turn off the water once the siphon starts as it should be self sustaining.) The bottom part is actually a valve which when closed will simply send water from the faucet to the tank.
I did read on another forum that "mixer taps" aren't as common in the UK as they are in the US. Is that the compatibility problem? It might be worth it to engineer a temporary mixer tap you could use to regulate the temp of the water returning to the tank. Your local hardware store can probably help you with this if that's the case.
The rest of it is just vinyl tubing and plastic garden hose ends. In truth, you can make one yourself if you're willing to buy the parts and assemble it. The hardest part would be finding the gravel vac end, which I'll bet you can mail order if all else fails OR use some hose clamps on a standard gravel vac to mate it up with the main hose. (I did this when I worked in a LFS
years ago and we had to run or hose about 150 feet to a drain.)
Whatever you decide to do, good luck!