Can u use plastic ziplock bag with a snipped corner to pipe out eclairs? I dont have a round tip with piping bag

Why not. I've used that technique for years - shown to me by a chef.
And, no clean up ... just toss.

Absolutely! It is a great work around. :)

Give it a shot! That works well in a pinch for many applications and as long as your bag holds out (read - is not a cheap-o bag) then you're good. Snip less than you think you need to first, test the size out, and adjust as needed. Have fun!