Fish tank (Alameda W end of San Antonio)

Looking for any size fish tank for my daughter. She wants to save 3 platy fish someone has to get rid of. They are going to give them away or "flush" them.. (probably garbage disposal). We were talking about this post this morning and I kind of miss-spoke and told her they would probably have to dispose of the fish and then... "what do you mean"... and I had to tell her they were likely going to have to compost them.. anyway she's fine but wanted me to post to see if she could get a tank to save them. She said she would take care of them..