Test Plugs for Offset Toilet Flange

Hello,

I need to plug two offset toilet flanges for my rough in inspection. I tested them before I attached the flanges with a 3" plug, but the plugs do not work with offset flanges.

I tried using a balloon, but it popped out.

Are there any caps for toilet flanges?

Thanks,
Steve

I found my problem.. My test ball has a small leak..