@db11 said:
and once you're done on the computer, you have the rare opportunity to buy all of your required plumbing parts in a single go!
Absolutely, apart from the bit that you 'forgot to order/broke/spoiled/can't find' that you desperately need to get the system working at 11 pm on a Saturday night! (Couldn't see a smillie to show 'head in hands exasperation' or 'I wish I had never started this'!) However, it is always a golden opportunity to buy those nice, indispensable, tools that are essential to get the project done.