So I was thinking, i just got a new shower curtain and it is washable, water RESISTANT, and semi-see through. So whever i put it under the full force of the shower head there was a mist going through! that sparked something. If it were to "disappear" from the bathroom, i can sew cup pouches out of them. So then you can just pull the bag out of your purse, put the cup in it, get out of the stall, and wash it without people knowing. Its like a built in strainer!! I took pics of it-

A couple to show the visibility through the curtain (w/o flash)


a close up (w/o flash)

It is sorta hard to capture the beauty of this curtain lol bc it is not grey it is blue. And the close up is to show it is woven with plastic NOT MATERIAL COATED WITH A SEALANT.
i was thinking about making them and selling them, but jeeze anyone can get a shower curtain. lol
So if you can find this kind of shower curtain at your house then you can make a cup pouch/strainer : )
note-
make sure whenever you buy it, it says water RESISTANT, not water PROOF.
well anyway good luck with your pouch making!!
EDIT**
I did test it and it worked! so I hope you ladies make a pouch too. the water drips out in seconds. I really hope I am not the only one that gets to have the privilege of a built in strainer.