I put a low gate in the hallway that leads to the utility room. Missy Cat's food and litter box are back there out of reach from the furbabies. My two senior girls never bothered the litter box, but, the boys sure are interested.
If you put it on top of the washer, my question is: what do you do with the box when the washer is running? Maybe find a small table that has an edge around the top. I have one that I bought at an antique store. I'm sure if you think on it awhile you will come up with a solution that fits your situation.
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Joanne
Eli
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Eva
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Rosie(R.I.P. 1996-July 29, 2013)
Cocoa(R.I.P 1998-April 26, 2012):