Just returned last night safe and sound from a month trip to Portugal from UK. Used our tank throughout with no ill effects.
We did find and buy a flexible funnel and 5L bottle spring water to fill it with. Perfect, thanks for that tip earlier in the thread.
PS: once holiday head was firmly in place I saw a novice fill his big white from a hose so I followed his lead only to reflect later that the hose we both used was for cleaning/ filling the toilet. Didn't panic as I was carrying sterilising solution and did a full flush out. Hence buying flexible funnel.