I use most of these properly according to the original sense, but may have used, and certainly heard/read ‘down the pipe’ as meaning something arriving later, and have read ‘wet your appetite’ without it sticking out as being wrong.
‘Happy as a clam’: I’ve taught this as a fun lesson in trivia to students, along with ’ as busy as a ___ ’ (bee) and 'as greedy as a ____ ’ (pig), which they usually get; ‘as big as a_____’ (house/horse), to which they invariably reply ‘elephant’; ‘as quiet as a mouse’, to which they indignantly reply that mice aren’t quiet, probably having confronted the issue directly.
I never knew that ‘happy as a clam’ came from ‘happy as a clam at high tide’. I always explained it- guessing- that a clam looks like it has a wide smile.
Usually when you say “blood is thicker than water” you mean that family ties are more important than other ties, such as those you form in your own. The “original” supposed meaning is the opposite — that the ties you form with those around you are thicker than the ones you have by nature of your birth. It’s disputed, but, like “Jack of all trades”, I enjoy throwing it out there
Edit to explain “Jack of all trades”: it didn’t originally have the ending “master of none”. It was supposed to be a compliment to someone who could do a wide variety of things. Now it’s often seen as a negative, especially when people tack on “master of none”. So at some point it got extended further to have some variation of “Jack of all trades, master of none, but better than being a master of one”.
I’m surprised “Fine toothcomb” didn’t make the list. There is, apparently, a theory that there is in fact such a thing as a toothcomb and therefore both “fine toothcomb” and “fine-toothed comb” are valid variants.
That’s the “fine-toothed comb”, I think. A “toothcomb” is - or so I’m reliably informed by Google - a structure that certain animals have in their mouths for, uh, combing themselves. Either way the phrase works.