Why not just use bulkhead fittings? For
example at US plastics (probably not the one you want, so just for illustration).
Cutting threads into acrylic plastic is a bad idea. The threads are stress concentrators (particularly when cut rather than molded - same issue as cut vs rolled threads in the fastener world only acrylic is a lot more fragile), acrylic is brittle, the screwed in barbs work like lever arms. Then there's the whole notion of a
tapered fitting in acrylic. The point of tapered fittings is that both male and female pats deform a bit to remove leak paths. Only acrylic doesn't deform - and we're back to those stress concentrators. At least use nylon barbs if you feel you really have to do it this way (I'm assuming it's an appearance issue)... Or go with BSPT (not tapered in spite of the "T" in the name) threads and fittings. This'll require sealant, but so will the NPT fittings if you're gentle enough putting the barbs in that your acrylic is OK. Not that any of us are working with pressures high enough to need much sealing. BSPT fittings also have the advantage that you can thread them in all the way to the shoulder, so some of the side-force from the barb is taken by the area around the threads (where the shoulder contacts the acrylic) rather than by the threads themselves. You can get BSPT nylon barbs as well (I'm going on about nylon because it's
softer than acrylic)