After looking at several solutions to the sticking slider this weekend, as mine had become impossible to use, I poured just a little olive oil onto the dried top of the slider. The black flat surface at the bottom of the bowl looking inside the basin. I slid it open once and it moved like silk. I know this will have been dealt with loads of times but not needing to know before, I had not read what to do. Warning! Use only Olive oil or Thetford/Dometic lubricant.