If it would rain strong now, since the concrete is not hard enought and "special" construction not finished, if filling complet, the tank would to 80% break appart (not alone because build on soft ground without removing the trees huge mass of roots: the tank actually does not stay on the ground, statically, but is hanging between the rocks) and this being the reason, the region may possible need to wait another 1, 2 days, if the Rain-Devas wishes so, for a huge raining to come at perfect time.
The filling of water in Nyoms tank from last year, will provide some water for the rest concrete possible to make and 1, 2 days light shower for two. Then it would be perfect timing as well, all tanks empty for the very first time. No worry so far.