What do you mean clogging up the pipes? Are you talking about the water inlet line? Overflow line? or 4 inch pipe? The roots will always try to get into the inlet line, and overflow. But if you designed the system with maintenance in mind, that should be easy to take care of. But after rereading your original post I'm assuming the system is a NFT system because of the statement about it being a continues flow system. In which case I can see the roots of such a large plant for sure getting large enough to dam up the water flow, and can be a problem if so. I have grown 6 foot tall plants in 4 inch tubing, but as a flood and drain system. It shouldn't be to difficult to convert that NFT system into a flood and drain. Just adjusting the water inlet, and overflow lines, then add a timer. Possibly larger reservoir. A 10 foot section of 4 inch tubing can hold about 5 gallons of water when flooded. So 4 of them would likely take about 20 gallons to flood the system without running the
pump dry.
Then taking into account how much water the plants drink daily. Not to mention the size (when full grown), and amount of plants in the system. A general rule of thumb is small plants like lettuce should have a minimum of 1/2 gallons of
nutrient solution per plant. Medium size plants should have a minimum of 1 to 1 1/2 gallons of nutrient solution per plant. And for large plants like tomato or melon plants should have a minimum of 2 1/2 gallons of nutrient solution per plant. So adding up all the plants as well as minimum requirements for them all should give you a starting point of the reservoir size you'll want/need.
P.S.
I wouldn't worry about only having male flowers just yet. Myself I prefer the ADS tubing over PVC, mostly because it's easy to find, and it's lightproof (black inside). It is a little more flexible than schedule 40 PVC, but as long as the stand is built to support the weight evenly, that's not really a problem for me. But because my ground isn't exactly even/level itself, leveling the stands can take patience. But leveling the stands would need to be done for both ADS, or PVC type tubing.