Would a large turkey baster work as a gravel vac for a 1.5gallon?
And to answer you marie, I think it would depend how disturbing it would be while you cleaned it. If your fairly cautious, and don't bumping around, just a smooth motion, I would think it would be alright. I clean my betta bowl's with them inside, I just am careful not to stir them up to much*twirlysmi
If you have a really aggressive betta who goes after the vac though, than I would take him out and place him in a betta cup if you still have that laying around?