I got my pool (a La Bassine) used from a friend who labored in it but didn't deliver in it. She had a liner in it when she used it, but I disinfected it really well before we used it. I did use a liner as well, and honestly I didn't even notice the liner - didn't bother me at all. I don't think it's as much an issue for disinfecting it later, as much as ease of cleaning it out right after birth. It was easier for DH and the midwives to drain the pool and then just gather up the liner and toss it, deflate the pool (which was then totally dry and clean) and stuff it away to be disinfected/folded up later. So we'll be using a liner again this time, just for one less thing DH has to deal with. But if that's not a big deal to you, I don't think a liner is at all necessary for sanitary purposes.
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