no-hub coupling for vent?

I picked up a 4" to 2" no hub coupling to use to convert my old CI stack to a 2" vent for a toilet and as I was putting it on it said for drain and sewer use only. Does that mean I should not use it for a vent?

It is an all rubber coupling with metal clamps.

If not what are my options?

I was thinking maybe a 4" nohub with metal clamp to a 4" bushing reducer to 2".

Other ideas?

Thanks.

I would think it meant drain and sewer usage vs supply line usage, and thus would be fine for your vent. But I'm not a pro.

coupling

Their intention was to tell you that it is only for sewer or drain use when under pressure, as opposed to the high pressure of a water system. The vent is not under any pressure so it will work there also.