From the package: Try on for size, then wash before use. For added protection, position a Simple Solution Disposable Liner (Optional, Sold Separately) in the diaper's mesh area. With the liner in place, slip you pet's tail through the hole and position the diaper between her back legs so that it's snug against her underbelly. Adjust the diaper wings up towards her back and position for a secure fit. Replace disposable liners s needed. Simple Solution Diapers are easy to wash and dry! Just attach the adjustable strips to prevent snagging. Wash the diaper separately in warm water on the gentle cycle and line dry.