The only way we got to sorted was pray control.
You do need to block all gaps into your house from the outside, but once they're in they have probably burrowed underground under the floorboards and can easily access the wall cavities therefore have full access to the entire house.
The strong poison pest control uses will kill them very very quickly. There will be a horrific smell for a week or 2 then you need to concentrate on closing all access points into your home.
We had a drain inspection which was thankfully clear and just put it down to gaps in the brickwork and patio. Once they were sealed and the pest controllers did their thing it was resolved very quickly.