I am installing an upflush toilet system in my basement. It calls for a 3" Vent line. Since I am going from the basement and up two floors to the attic, can I reduce from the 3" Vent line to a 1 1/2" vent line.

With a sewage ejector system you need two vents. One for the fixtures and the other for the pit. The pit vent MUST BE DEDICATED and not connected to any house vent. It MUST go outside by itself.
If your system only calls for one three inch vent I want the brand name and model number of your unit. Regards, Tom

Can you give us more info as to what you are calling an upflush toilet? Most areas require a two inch vent for toilets(inch and a half won't meet code anywhere I know of) Also, vents can only be increased insize, not decreased in any way.
As Tom stated, if you are talking about a sewer ejector, the toilet must be vented with two inch, and the ejector pit must be vent also with two inch(for residential applications). I can't see why you would need a three inch vent for either. Let us know more about your setup, and we will do our best to give advice.

What name brand upflush toilet are you using? Any upflush systems I've ever used require an 1.5" or a 2" vent... unless the overall length from the basement to the roof exceeds a certain distance and then I guess I can see a required increase to a 3" vent.

Tell me the name brand and hopefully I can tell you more, but for now I will tell you that these upflush systems can be very finicky at times. At this point I would recommend that if the system call for a 3" vent... you want to run a 3" vent.

Let me know more and we can discuss better... OK?

MARK

I have a BurCam Easy Flush System. Yes, it calls for a 2 in drain but a 3" vent. The only reason I thought about an 1 1/2" line is that's what was used in my house until it got to the attic/roof, then it went to 3".