I think your skimmer tube go buy a longer tube an connect it to a big pail
My pail size about one salt bucket, went overseas for a week,come back the bucket is only like 15% full
As for top up water, fill the sump tank with more water the night before, of course if have ATO is best
Anyway for me, sump tank still a lot of water despite not using ATO
Can go invest on one IP camera to view your tank in case anything happens...