Of course, you have to be a real estate agent to do this. I’m newly licensed (slight career shift in progress) and I sat my first open house. It was an unusully blustery, snowy, blizzardy day and no one showed up. I went to the car and got my Bloomfield-tweaked Gen and worked on Merrily Kissed the Quaker’s Wife and Rights of Man in a vacant house. It was kinda fun. Though I’d rather have had people show up.
Empty houses sound way cool. When we closed mom and dad’s house, I piped Amazing Grace as I walked from room to empty room. Upper octave was even better - I was about half-deaf by the time I had worked it all out of my system.
Mark
Yeah, empty rooms (with no carpet) are great. We’re in the process of replacing all the carpet in our house with laminate flooring, one room at a time. I find I like to practice whistle in the empty rooms after I’ve removed the carpet… bare walls and plywood subfloor really bounce the sound around. 
I got to do that once with our house before we moved in.
Even now, the living room sounds pretty good, but the kitchen/breakfast nook are fantastic, with high ceilings and nothing but hard surfaces. Even my least favorite whistles sound great in there.
Unfortunately when I was a realtor I hadn’t gotten smart enough or brave enough to try the whistle. However, I can recall those many hours sitting in an open house wishing I had something to do besides wait for a tire kicker to pull in the drive.
Now I’ve got my whistles, I don’t sell realestate (except occasionally my own) and I only wait on my loving spouse.
I’ve always found that playing in the bathroom (which has great acoustics) sounds neat. I’ve done it a couple of times with my guitar. But I’ve yet to do it with my whistle…don’t want to break any mirrors 
I find that when I play my whistle in a hallway that offers good acoustics, probably similar to an empty house. Playing in the bathroom. Well, I wouldn’t play for too long! The bathroom is not a good place to monopolize 
. I’m just imagining my dad and my brother going nuts outside waiting to use the facilities while I whistle away Donnybrook Fair or something 
LOL Well I wasn’t suggesting that people hold up the bathroom. If you’re in an empty house, hang out and play in the bathroom
And yeah hallways have great acoustics too
Gee - I though it was just me. I’ve been “trying” to play over the past two months (going pretty well actually). When my wife and kids are out I go to our upstairs hallway. We have a house that was built somewhere in the 1870’s - about when Wild Bill Hickock was being run out of town for shooting his own deputy (sorry-I digress).
Anyway the accoustics there due to the high ceilings and solid wood floors is really haunting. The high D’s take on a different character in that space and what I can get out of the low D’s sounds pretty good.
Ive just got two new whistles (I’ve got whoa bad) - a Cheiftain in G and a Sunslinger in A. They sound especially surreal in the hallway.
Now - If I can just figure out how to get the keyboard and extension cord out there…