I see a lot of small 2l expansion vessels fitted horizontally and a few with the water connection at the top, in the legionella advice it mentions having water connections at the base for draining and flushing, also so no debris falls into vessel. From a practical view if the membrane breaks inside then air could escape offering no expansion, I've tried researching, a lot are from Italy but are vague on fitting position, although a couple stated vertical with water conn at base. What do you think?