Very easy to change the diesel tank.
It's held in place against the chassis by 2 steel straps, these have a bolt through each end, support the tank before undoing them as a big plastic tank to the noggin tends to sting a little.
There is a rubber pipe used as a filler neck, this has jubilee clips fitted at either end, I recommend undoing the the top clip (slightly more awkward to get at) and then clamping off the pipe to prevent any remaining diesel from splashing out onto you. While your there, you'll also see a thinner rubber pipe which is the tank breather, undo the jubilee clip near the filler neck and swap it once you have the tank off.
Once those are sorted, lower the tank slowly!
As you lower it, the securing clips for the diesel feed and return will become visible. unclip the pipes and lower the tank further.
You should now be able to get your hands on the fuel senders electrical connection and the push fit connections on the feed and return. Squeeze the edges of the connectors to release the pipes and be mindful of the impending fuel leakage as you pull the pipes away from the tank. The are different sizes so can't be mixed up.
If your swapping the sender over, I strongly recommend a new O ring seal as water ingress into the tank is not very desirable !!!!!!!
All in all, thats an hours work
Have fun.