Huge special tap is out for acrylic, it would almost certainly shatter.
If you are dealing with extruded acrylic forget it, it will stress crack almost immediately; you must use CAST acrylic.
If you have a CNC mill that is capable of helical interpolation you can thread mill. This could be a preferred method because the cutting load is low.
If you do attempt it in a lathe hold the acrylic tube inside a closely fitting split sleeve made out of aluminum and nicely polished inside so it will not mar the acrylic.
Acrylic machines, or thread, okay at low speed but your tools have to be ultra-sharp, carbide insert threading tools are not suitable you should grind your own in HSS; remember zero top rake for acrylic.