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Great suggestion, especially since Barkeepers Friend does not contain chlorine bleach which can permanently damage stainless steel, especially thinly-coated "economy" sinks. The active ingredient is oxalic acid. Another product with a similar chemical composition called ZUD that I have also used successfully. Both of these products are available at most hardware stores… sometimes side-by-side!
Just remember that stainless steel sinks can scratch, even with "mild" abrasives such as these products. So don't overdo the scrubbing!
Thanks for the suggestion. I don't know how I could have forgotten about Barkeeper's friend, a mildly abrasive but chlorine-free bleach I have often used. One great thing about Barkeeper's friend and its cousin, ZUD, is that it actually dissolves iron rust and rust stains, making it great for removing discoloration on porcelain sinks and tubs!
Obviously removing all urine-soaked wood is the most thorough solution although probably not necessary. Removing the saturated particleboard was a definite must, as particleboard absorbs moisture like a sponge but does not seal well. There was nothing you could do to permanently ameliorate or eliminate the odor.
Clean the wood plank underlayment with a cat urine-odor removal/neutralizing product. When completely dry, coat the planks with a few coats of a waterproofing sealer or polyurethane. This will lock in any residual odor. Then reinstall particleboard or plywood to restore the level of the floor.
I have done this a few times in some rather malodorous situations and the results were excellent. But again I must emphasize that I don't suggest this quick solution for other than lightly stained materials.