There is no way you should have to empty the toilet flush tank, the toilet cassette or the hot water tank to stop them leaking in transit. I usually empty the loo but that is all. I think you should bare in mind the additional weight though.
I had big problems with my suspension as all the weight was on one side of the van, all the latter plus the battery, fridge (and contents) crockery and cooking stuff, oven, heavy shower cubicle, charger, water heater, microwave plus whatever bits in the overhead lockers.
On the other side we store the bedding,some food and drink and in the rear, the wardrobe.
Result offside suspension sank.
Despite the van being in warrenty, I ended up paying...it's a long story.
However, I did check the overall weight and weighed everything individually. In my opinion it was extremely difficult to achieve balanced target weights, especially nose weight even carrying the minimum of equipment.
I visited a dealer on the pretence of knowing nothing about vans and admired the front locker with room for two gas bottles and a spare tyre provided.Yes, no need to run out of gas he said! When I came clean and told him I had problems with the same make and model of van he told me that of course, he always emptied his hot water tank and moved all the contents of his front locker into the car for travel purposes . Er, what !
Come on manufacturers get it right, you want to sell vans full of goodies but then put them on chassis that are not built to take the weight.It's not that they are not available.
Dealers must think we are totally gullible if we think that the excuses they give are justifable.Or maybe we are.
Should we really have to sit down with a dealer and go through every eventuality about what we can or cannot do? I accept that a certain amount of common sense has to prevail but come on.
Maybe it's time the manufacturers gave three weights,
1)Empty weight
2)Empty weight plus two full gas tanks, one battery, full water heater, full loo flush tank, spare wheel.
3)Max permissable weight.
We can then be assured that the van has been designed to take what I consider necessities, and we then have a clearer idea of what we can actualy carry in addition.
As for the leak in the loo tank tell the dealer that it is no acceptable.