As others have said it is important to clean the area correctly ..... as far as your cat is concerned. Normal cleaning solutions do not get rid of the smell that attracts them back to toilet in same place. Look at links that have been posted. It may all seem a faff but it's worth it to stop it recurring.
BTW. Ask vet about this problem by all means but, if Feliway/Zylkene suggested, buy it online. I got 30 Zylkene capsules from vet for £18.63 and then bought another 30 online for £10.80. Hate to think how much the difference would be on the Feliway.
Zylkene is a supplement rather than a drug which is supposed to chill out your cat. Difficult to tell if it's working as I'm giving it to Dinah who stays out alot (her choice entirely as has 24/7 access) so she does tend to sleep when she comes in anyway as she s very active.
I got mine from Pet Vet Care Online
www.petvetcare.co.uk The Feliway product imitates natural pheromones that again are aimed at chilling out your cat. The plug in (plugs into any electrical socket) takes a while to take effect but the spray is more immediate. I got the spray for £12.34. I have to say I do rate the Feliway product.
I only started using the spray on Friday and so far have only had 1 pee in bath. That sounds bad! You know what I mean!