I kept several in pots for a couple years - I had harvested from a plant on the family farm. The largest was 3-4'. Planted them last year. Only one has bloomed since transplant, but I understand that sometimes it takes a couple years after transplant to bloom. It may need more water than if it was planted.
Good luck!

I have to say that I don't know much about lilacs, but I would suggest pulling the plant out of its pot to check the roots. If the plant is root bound now, it will be even more so come fall. If this is the case then move it to a bigger pot. Also, it seems like there is something that you could do to help the pot retain moisture so you don't have to water everyday. Like maybe partially bury the pot in the ground or a mound of mulch.

Is there supposed to be a picture with the original post?

- Brent