Not sure where you live, but in the USA one can get an enema bag at any drug or discount store. It is "old fashioned", but still available.
The only danger is doing too many enemas and getting "addicted". Your colon could get out of practice in normal eliminations if you do them daily for an extended time.
It is either time consuming or expensive to do a wheatgrass enema, so I would start with plain water until you get the hang of it. Do the wheatgrass enema when you're good with the equipment and learned how to hold the liquid internally for 5 minutes or so.
Grandma knew how to do these things, but we have to learn for ourselves.