OK, the tank is on its side (horizontal). The photos don't really show this. I presume (if the mounting feet are at the bottom) that means the hot water connection is at the top, which would put the cold water inlet (with the drain valve) at the bottom?
The intake tube for the hot water outlet runs almost the length of the tank, inside the tank and should be parallel with the top/sides.
I *know* this because I have just replaced my 60 litre tank with a brand new one at over $1000 because I couldn't get a usable amount of hot water from it. Once I got the new one and looked inside, then compared it to inside the old one, I could see that the old intake tube "drooped" towards the bottom of the tank. Everything above the low end of the intake tube was air only, and the volume of hot water less than litres only.
The attached photo
shows a stainless rod inserted into the tube, to show the drooping angle.
Long story, but frustrating and largely unnecessary! Hopefully someone else can learn from this