It drains beautifully and smells HORRIBLE unless you bed deeply! I try to bed deeply enough so all the pee get soaked up in the bedding and doesn’t make it to go through the stall savers, because otherwise it stinks.
I also use barn lime to neutralize when they are in. Honestly I keep my horses out so much it’s hardly relevant any more…My show horse stayed in one night this winter, despite subzero temps a lot of the time. The night he stayed in I had a late lesson and it was 35 and raining, so I left him in for my convenience.
I would NOT do the stall savers again because of the smell, and because really big horses punch holes in them. I had an 18h WB boarder who tore the crap out of the bottom of his stall. I had to put mats over the stall savers. The base was good though! sigh. I ended up closing my barn to boarders last summer after 5 years with the setup in heavy use, and never solved the stink issue other than heavy bedding stalls which is $$$$$$. Not sure what I would do if I was doing them again. The stall savers do fine with enough bedding and not too heavy of horses on them, but the bedding issue is real and expensive for a professional program. As I use them (for cool down after I ride, to let my horse chill for an hour in his cooler with hay), it’s fine as is for now. Someday I’ll put in a stall mattress system for him maybe.
My climate is midwestern seasons (northern Indiana).