Reservations about reservoir

Having a jojo tank really is only a temporary solution to capturing water for non-potable use. After all, when it is full, it means the garden has been watered by the rain already, so there is no need to further empty it in that area. Depending on the size of the tank and its situation, it may not be practical to decant into 5 litre bottles and take into the house for flushing toilets. Ours is an outsize 5000 litres - equivalent to more than half of two weeks' household usage by a family of four - and requires a walk down 13 steps, round the house and lugging 10kg at a time back round the house and up the 13 steps. If you have survived the trip and then try to flush a toilet from the bottle, you will soon find out what splash-back is. So a bucket really is the answer, but who wants a line-up of 50 ten-litre buckets outside the door?
You can also use it for washing cars, but as a dirty car has become a symbol of showing how much you care about saving water, you don't want to attract pariah status by letting the sunshine blind other drivers as it reflects off your immaculate paintwork. Not that I was ever one for rabid wash-and-polishing even in those distant days before the drought.
A measure of the severity of the drought is that the tank took seven months to actually reach capacity the first time, and the sudden onset of a little late winter rainfall has meant that I haven't been able to reduce it noticeably. After a wonderfully unexpected 20mm fell yesterday (forecast was about 7mm), I felt obliged to wend my way through the garden to fill a few more bottles and was peeved to note that the tank was seeping water from the join where the 'lid' is affixed. What kind of water tank allows seepage? This is not an old concrete dam in the Karoo. It is a brand-new, plastic (and hence indestructible) receptacle. Perhaps I have missed something, like a sign that says, Do Not Fill?
It looks as though I will have to attach a hose and water the garden in the rain in future just to keep the tank at a non-seeping level.
I estimate that should I use the 5000 litres it will be gone in a few weeks and, bearing in mind that we are supposed to have winter rainfall over roughly 4 months, once emptied we will have to wait for maybe 6 months before it fills again. So I have reservations about this reservoir.