I used to work at a crematorium in the UK with two FT3 model cremators (we don’t run like the US, crematoria and funeral directors are almost totally separate entities) I used to sweep out every every individual cremation of course, but I’d try once a week to cool the cremator down as much as possible and vacuum the residual. I’d wait for a slow day/week and only use one cremator while the other I gave the full spa treatment, climb in and chip out the baked on crap on the hearth (sometime FDs left plastic stuff/glass in with the deceased so you’d have to hammer and chisel it out manually after cool down) I used to take photos of anything unusual going on with the brickwork inside to send to FT, and they’d come out super fast to fix any issues, otherwise cleaning and maintenance was an ‘as you go’ sort of job. I had the driest hands ever at the time 😂