At the risk of being too personal and possibly biased. ( I'm a dog person.) Here's my mutts enjoying their swamp cooler.
From the top, my 15 year old Aussie mix. In the middle, our 14 year old dachshund mix. The last, is our 'new' dog, a 3 year old chow mix.
Last year I bought this Mastercool unit on Craigslist for $500. Cleaned out the insides and put a new pump. Works great. Currently blowing 70 degree air.
I had to pour the slab it sits on, which is 55"x55". I went a little crazy while preparing the 'hole' for the concrete and removed a couple wheelbarrows full of dirt to use around the yard for filling low spots, etc. I had lots of broken bricks and rocks laying around which I used to fill up some space in the hole I created. But even though, it was twenty-nine 60lb. bags when I was done. I had 22 bags on the premises and had to run to HD for another 10 bags before the concrete set up. Learned some things on that one....
I use a bleeder hose on my unit. All of the water that is bled is fed by gravity to the dog's swamp cooler, where it is used again. I just removed the float since the water is under little pressure. I also have a bleeder on the smaller pump and that one gravity feeds to the navel orange tree on the front corner of my property. I figure if I 'use' the water 3 times, then I can justify the bleeder system.