When I recieved my TBS, I laid it out on a tarp for about 30 minutes. I heard some poping noises and in true nubie from thought it was barnicles or the bivales complaining about the lack of water.
Oh no, was I wrong. So leave it out, be patient.
Mabey having a spray bottle of tank water handy to wet down corals and sponges would be a good way to go. I am certain that, had I known what the poping sound was, and waited long enough, I would have found every last mantis before it got in the tank.
But, if you think you want one, use the Splach method with seltzer after you find their hiding spot. The hyper-saline method isn't not going to be kind. Either one seems to coax them out, but you have to find them first. When I pulled the targeted rock out the other night they stared poping righjt away just like when I got the rock so be patient.