Not if you want it to work.

The air must be allowed to rise up the vent or it will suck into the pump.

Personally I would only use the Essex flange.

[quote author=flux  link=1133631757/0#2 date=1133641026]the side outlet says it is for the vent on the packaging and the top for the supply to prevent air being pulled in,the top outlet is connected to the extended tube,if the side  outlet is for vent and gravity flow ,do you have to have any gravity service or can i use it just as vent?. [/quote]

http://www.techflow.co.uk/qtinstall.htm#fig2

see fig 2. and do not alter it.

the air rises in the cylinder as the water heats which is why you have the dip tube into the water, see sketch.

Yes thats ok, However I would recommend the wc cisterns do not as the pump will cycle on and off when it's filling