As one of the new guys on the block, my opinion may not be realistic, but here it is. If I looked at at floor drain and the grid did not appear clogged, I don't think I would take it any further. If if saw signs of flooding/clogging or if the grid appeared impacted, I may poke a screwdriver into it to confirm. I don't think it is my RESPONSIBILITY to do an exhaustive test as much as it is my RESPONSIBILITY to reccommend repair. OK, dumping a gallon is a nice gesture, but it reallly doesn't tell you much and having dumped a gallon, aren't you then liable for testing it and not determining a problem? What if it needed two gallons or six? Or running a hose for ten minutes? When you test something I think it should be a reliable test or don't test it at all. How many of us run the water and then inspect the house trap to see how it is flowing? Would we know if all was running through or if some water was leaking underground? Likewise, when walking a roof, if the gutters appear clean I am not going to attach a hose and drag it up to the roof to check for clogs either. Nor am I going to run the water on the roof to check for leaks. And if I see a common crack in a foundation wall and there are no signs of a leak, I am not going to flood the yard to see if it is leaking. I believe that the basic home inspection is a game of visual clues and simple non exhaustive tests. The better you are at recongnizing these clues... the better you are at being an HI. If I am wrong, and in a very humble fashion, I concede that there are inspectors on this site, that if they tell me "Steve, you are wrong, you should always test floor drains by running x amount of water through them" I will shut up and consider it something new that I learned here today. Now there is no test or no limit that I am not capable of doing or arrange to have done... for a fee.