There is a plastic compartment with a sliding cover that you place the
tablet in. Last couple of washes it's not opened, so the wash has only
been
with plain water. Leaves a soggy 7/8 of a tablet.

If you don't use prewash, you can just put the tablet directly in the
machine. The door is only there to stop it falling into the soon to be
discarded water during prewash.

Christian.