The only option I see on bittrex is btc to zec. I do not show zec-btc therefore is it true I cannot trade zec-btc there?
You can sell zcash in bittrex. BTC-ZEC only refers to the "market".
There are two buttons one for selling and one for buying.
You can see it here.
https://bittrex.com/Market/Index?MarketName=BTC-ZECLook on the bottom right corner.