Cleaning portabello mushrooms

I don't remove the gills. (haven't made stuffed mushrooms yet). Against all advice, I do wash or soak them. I spin dry very well and/or pat with paper towels to get rid of excess water.

I don't clean them unless they have little bits of dirt attached, and then just brush them. Leave on the 'gills'.
While you mentioned they're sliced, the only time I do 'clean' out the big caps..is when I stuff them.
Using a 'tomato shark", or melon baller, or grapefruit spoon to scoop out the gills.
But I save those and incorporate into the stuffing mix.

I never clean the gills...to me, not worth it!

I do not trim them...if you were going for a "clean" look, you could use white button mushrooms without the work, but also without as much flavor!